1. IBM’s legacy ofusing Tab for field navigation
"Tab also has typamatic capability that allows you to move the cursor quickly from field to field." – ch_123
2. Enter key overloading creates user confusion
"The overloading of return to either send a message or add a newline has become really annoying since chat apps (and then now AI) have become popular." – bsimpson
3. IBM’s internal CUA politics and patent reasoning
"I would guess that using the tab key in this way was part of a patent they were pursuing and Microsoft's use would show this to be 'obvious' and thus not patentable." – rbanffy
4. Modern key‑binding inconsistencies (Enter / Shift‑Enter, CapsLock)
"Shift+Enter will usually enter a newline in a message without triggering send... No guarantees on specific applications, just my own experience with this." – tracker1