Actually both tapbacks (for a long time) and reply threads (since the latest iOS release) are both supported in MMS group conversations. The iPhone will send a tapback as an SMS message such as "Liked 'contents of message that was liked'" and other iPhones convert that back into a tapback. Google Messages also does this (and in fact did it before Apple did). iOS does not convert Google Messages style tapback messages into tapbacks though, so iPhone users only have half of the solution.
As for reply threads, when it's used it creates a lot of confusion for non iPhone users and it's not clear how Google Messages and other texting clients can fix it post-hoc. I'm not even sure how iOS reconstitutes it-- perhaps Apple sends some message metadata on the side via iMessage?