Preference, no, you’re right. Convenience - why not? If a priest is extremely elderly and incapacitated then it certainly might be more convenient for him not to distribute communion by himself, but he may let others do so while he sits down. That sort of convenience is perfectly good reason to ignore a Church ‘preference’ that priests distribute communion themselves.
Why are you so intent on assuming the worst - ie that all else IS equal in most situations where priests consecrate lots of hosts and that they are DELIBERATELY choosing to go against the Church’s preference? For starters I’ve seen plenty of churches that seem not to resort to the Tabernacle before Communion at each Mass - including those that use the method where individuals will place their own unconsecrated host in a bowl at the Church door before entering so the number is approximately right.
Neither you nor I are privy to all the possible reasons why priests consecrate the number of hosts that they do. Nor does a priest need to explain his reasons to you or anyone apart from his Bishop should the Bishop become concerned about it.
At least one situation where I can see it making lots of sense is that of large Churches with many Masses of a Sunday. One chuch in this diocese has 11 Masses each and every Sunday.
See, attendance at each particular Mass in such churches can vary dramatically from week to week, I know this from my own experience. A Mass time that is packed one week can be much less well-attended the next. And vice versa. So there’s simply no way for a priest of judging with any accuracy how many people will turn up at a given Mass on a given Sunday.
And the priest always needs to consecrate enough so that he won’t run out - and it’s not like in a large Mass he can a) take tiem out to get an accurate head count of the congregation AND b) painstakingly and timeconsumingly measure out with exactitude the number of Hosts required. So the end result will frequently be excess.
Rather than go through the wasteful process of consuming ALL the excess hosts after EVERY single one of those 11 Masses - it makes incredibly good sense to reserve the remainder from the earlier Masses instead, so that priests at the later Masses can safely consecrate lesser numbers of Hosts.