Well, if you search for these projects yourself and read the first few paragraphs on their websites, you might learn the selling points. Warp has a lot of features that are just not possible in urxvt.
1. I wouldn't say there really is much that would be "just not possible" in urxvt. If you drop down to Perl level, you can do almost everything (albeit you would have to write Perl).
2. The reason urxvt doesn't have majority of those selling points is because they arguably aren't the concern of terminal emulator at all. Things like better autocomplete menu, command editing, history browsing etc. historically fell under purview of the shell. You can have all these things with say zsh and a few chose plugins.