One thing that keeps them from doing it is that the bishops themselves don't really know the Western rite. They don't use western vestments, and they don't celebrate it. Even some of the priests who are in charge of the WR are in Eastern rite parishes. And I don't think the Western rite clergy and laity have much interest in developing new liturgies - most of them fled from such activities in the Episcopal and Roman Catholic churches.
And the "Latin patrimony" rite has always been an Orthodox rite. The pre-schism Roman rite really isn't much different from the Tridentine rite, which is where the Liturgy of St. Gregory came from. There were a few changes made to it by the Antiochian Archdiocese: deletion of references to merits of the saints (1), deletion of the filioque (2), and insertion of an epiclesis (3). Guess that's what you mean by 'doxified, although (1) and (2) were certainly present in pre-schism Western liturgies and creeds and (3) was generally absent from them (at least in the Roman tradition).
If the presence of 1 and 2 and the absence of 3 in the Western Rite was not originally a hindrance to full communion between our Churches, why are they now considered unacceptable if they existed before the schism?
You assUme that they were acceptable before the schism. The reaction to them demonstrates they were not, e.g. Pope Leo putting up the Creed (the one without filioque) on the doors of St. Peter's and in St. Paul's with HAEC LEO POSUI AMORE ET CAUTELA ORTHODOXAE FIDEI» (I, Leo, put here for love and protection of the Orthodox Faith). They are, after all, what led you into schism.
Take for instance the epiclesis: the Roman rite, according to, for instance, the "Catholic Encyclopedia" had one:http://www.newadvent.org/cathen/05502a.htm
Epiklesis (Latin invocatio) is the name of a prayer that occurs in all Eastern liturgies (and originally in Western liturgies also) after the words of Institution, in which the celebrant prays that God may send down His Holy Spirit to change this bread and wine into the Body and Blood of His Son...It is certain that all the old liturgies contained such a prayer...Nor is there any doubt that the Western rites at one time contained similar invocations. The Gallican Liturgy had variable forms according to the feast....The Roman Rite too at one time had an Epiklesis after the words of Institution. Pope Gelasius I (492-496) refers to it plainly: "Quomodo ad divini mysterii consecrationem coelestis Spiritus adveniet, si sacerdos...criminosis plenus actionibus reprobetur?" ("Epp. Fragm.", vii, in Thiel, "Epp. Rom. Pont.", I, 486). Watterich (Der Konsekrationsmoment im h. Abendmahl, 1896, pp. 133 sq.) brings other evidences of the old Roman Invocation. he (p. 166) and Drews (Entstehungsgesch. des Kanons, 1902, p. 28) think that several secrets in the Leonine Sacramentary were originally Invocations...It should be noticed that the Epiklesis for the Holy Eucharist is only one of many such forms. In other sacraments and blessings similar prayers were used, to ask God to send His Holy Spirit to sanctify the matter. There was an Epiklesis for the water of baptism. Tertullian (On Baptism 4), Optatus of Mileve ("De schism. Don., III, ii, VI, iii, in "Corp. Script. eccl. Latin.", vol. XXVI, 69, 148, 149), St. Jerome (Contra Lucif., vi, vii), St. Augustine (On Baptism V.20 and V.27), in the West; and St. Basil (On the Holy Spirit 15.35), St. Gregory of Nyssa (Orat. cat. magn. xxxiii), and St. Cyril of Jerusalem (Cat. iii, 3), in the East, refer to it.
At the time before your schism
That in the Liturgy the Invocation should occur after the words of Institution is only one more case of many which show that people were not much concerned about the exact instant at which all the essence of the sacrament was complete. They looked upon the whole Consecration-prayer as one simple thing. In it the words of Institution always occur (with the doubtful exception of the Nestorian Rite); they believed that Christ would, according to His promise, do the rest. But they did not ask at which exact moment the change takes place. Besides the words of Institution there are many other blessings, prayers, and signs of the cross, some of which came before and some after the words, and all, including the words themselves, combine to make up the one Canon of which the effect is Transubstantiation. So also in our baptism and ordination services, part of the forms and prayers whose effect is the sacramental grace comes, in order of time, after the essential words.
but of course, the scholastics could leave well enough alone
It was not till Scholastic times that theologians began to discuss the minimum of form required for the essence of each sacrament.
and then got it wrong
It seems that an early insistence on the words of Institution as the form of Consecration (see, for instance, Pseudo-Ambrose, "De Mysteriis", IX, 52, and "De Sacramentis", IV, 4, 14-15, 23; St. Augustine, Sermon 227) led in the West to the neglect and mutilation of the Epiklesis]
which progressed to a problem
This form has given rise to one of the chief controversies between the Eastern and Western Churches, inasmuch as all Eastern schismatics
now believe that the Epiklesis, and not the words of Institution, is the essential form (or at least the essential complement) of the sacrament.
whereupon, instead of correcting the matter, the Vatican
decided the question by making us kneel and adore the Holy Eucharist immediately after the words of Institution, and by letting her old Invocation practically disappear....and the disappearance of any real Epiklesis in our Liturgy confirms this
IOW the Vatican persisted and refused correction and decided on heresy, going into schism over it. Since it chose that over full communion with the Church, the lack of an epiclesis, or at least a full one, and the concommittant defense of lacking one, prove more than a hinderance for the Vatican to return to Catholic communion.