Literally everything about animate. It is hugely bloated and awful to use and crash prone. It takes upwards of 30 seconds to save a file. It has two different kinds of tween to support backwards compatibility. And the "HTML" export is a garbage fire. Flash used a form of vector graphics that were incompatible with svgs.

Adobe has been trying to maintain backwards compatibility with flash (because most studios were still using the last version macromedia put out over 10 years ago) So adobe animate was always doomed to try and please everyone and end up pissing everyone off.