People can take the rules and bend them. Use errata or not. Hold true to Sage advice as if it were sacrosanct or an ad-lib. No one ever seems to debate this. Yet...
There is always debate.
The primary reason is D&D is a group game. And groups need to agree. So when you keep changing things, it has a tendency to make disagreements at the table. Not arguments, but disagreements. Things like, let's use ASIs or I am playing a yuan-ti. This causes consternation within the players and/or DM.
The secondary reason is the larger gaming culture. People like it when a culture is built. That is what D&D has done. But when you consistently change things, you are bound to upset part of the culture. Are the changes New Coke or getting rid of cocaine as an ingredient? Only time will tell.
PS - And for anyone that is about to pull up to the keyboard and use the "The DM has the final say" argument. Please... for the love of god... just don't.
I think they changed the cocaine thing because laws forced them to, otherwise we may still have the Coke in Coke today!
Could you imagine that! That might actually be a killer Coke (in some cases, quite literally) to drink. For giving one pep, the old recipe may actually be the BEST!
On the otherhand, no one need talk about New Coke...