Well, the central idea of the GG series was Lorelai's rejection of Emily's high society world and conflict between those two worlds.

And IMO Rory must have an opportunity to choose between those two worlds herself.
So, a suitor for Rory from "high society world" is almost a must in such a concept. Rory must have suitors from both worlds. There almost must be a love triangle for Rory between her suitor from Lorelai's world and suitor from Emily's world (for example Logan and Jess or Dean).

That's my view on the series. Besides, Milo was not available anyway, so they had to introduce another character in Rory's romantic life.