It’s also not the case that there is such a limitation.
https://support.apple.com/en-us/HT207006
A single contact / conversation can even mix and match.
Re:The Last Message Sent on AIM
by Andrew_nenakhov on Monday March 01, 2021 @04:46PM
(#26308887)
Are you really suggesting that SMS fallback is a good enough way to message people in 2021? How about sending them a video? Location? Voice message? MMS? Does this crap ever work?? (In my country it doesn't work between operators and costs €.5 for one message)
Whether this limitation is intentional is irrelevant, the UX is still bad.