Abelard was censured for having "published" (made available for dissemination) a book examining the nature of the Holy Trinity without submitting it to the ecclesiastical authorities for approval beforehand but never stood trial for heresy. His punishment was therefore in accordance with Benedictine rules for aberrations on the part of members and one which, upon resigning his membership, he could simply walk away from. Which he did.
However much the authorities might have liked to have tried him for heresy at the time they were unable to do so without calling into question the system they themselves had devised for dissemination of ecclesiastical literature, which in modern terms had been "subcontracted" out to emergent universities and seminaries as well as monastic institutions. Abelard's notions about the trinity were in fact not too dissimilar to others which had already been published with their approval. We have only Abelard's own testimony to go on but it appears that your assessment of local rivalries and jealousies is probably the most accurate in trying to gauge the motives behind his censure at the time of his first arraignment. Abelard had effectively walked into an ongoing rivalry between two camps (who also figure coincidentally in the "Who Killed William Rufus?" murder mystery), namely that which was comprised of the followers of the influential French abbot Suger and that which was made up of the "school" established by Anselm during his self-imposed exile in France twenty years before. Suger, who was allegedly a good friend of Abelard, had excited huge opposition from his fellow ecclesiastics during his meteoric rise in political as well as religious terms, and moreover he enjoyed the protection and patronage of the royal court. The Anselm school was a group of vociferous anti-Sugerians who had the patronage and protection of the French cardinals and who were constantly pressing for a monopoly on the right to authenticate, control and draw revenues from doctrinal works aimed at the major market. When they saw Abelard, a Sugerian who had established a huge reputation in his own right, attempt to bypass them it would not have been long before they called in the big guns to stop him. However it appears the cardinals balked at pressing for a full accusation of heresy and were content to chastise him and ensure that the book was destroyed in this case.