For slower speeds, like on modems, things become somewhat more difficult, as the protocols often have invisible assumptions about timing and performance that make it inefficient on links with very limited bandwidth.
Thus ARA was considerably more complex than similar solutions for IP, replacing many parts of the AppleTalk stack and seriously modifying others.
Nevertheless, ARA was the only protocol available for remote access on the Mac, and also shared the typical Apple properties of being easy to install, set up and run.
The introduction of SLIP and the increased use of IP on the Macintosh led to some infighting within Apple as the profits from ARA were reduced.
This led Apple to place their IP remote access software in ARA as well, although this had the side effect of making various freeware implementations much more popular.