Gosh, growing up we all called it the "2100 South Freeway." Calling it "the 201" was a concerted P.R. effort by UDOT (working with KSL and others).
Buyouts were pretty crazy for the new freeway interchange as it is (all the businesses south of the 21st South Fwy, east of 9th). The rail yard is huge and they were probably trying to cross it at as much of a 90-degree angle as they could (to reduce bridge length). Going diagonally to connect with I-80 would have just made the project a lot more expensive for minimal benefit. (But this is just my opinion).
The other way is to make I-80 diagonal by starting at 2100 South and then move down to the current alignment.
It is rather interesting that the eastern part of I-80 was built where it was. Obviously it lines up with where Parleys Canyon is, but why wasn't it routed directly northwest from there to connect with I-80 west of downtown and produce a continuous route? Most cities in the 1950s had no issues with tearing down city centers to build new freeways.
In fact, I came across an old planning document with a freeway that would have done exactly that...but it still didn't connect directly to western I-80. That was the proposed East Valley Freeway, which would have junctioned I-15 at 600 North, gone southeast through downtown, and then south generally along the 1300 East and Van Winkle corridor.

That explains both the weird asymmetry in the routing of I-215, the original configuration of the 600 North interchange with free-flowing ramps, and also probably why Van Winkle exists in the first place. For the sake of downtown I'm glad the freeway didn't get built, but it sure would have made accessing the east valley and especially the University of Utah area a hell of a lot easier.
(Also, it's fun to see what's on there that never got built and what isn't on there that did. The 20th East Expressway never came to fruition either, but the arterial "West Valley Highway" mostly got built as expressway, now-half-freeway Bangerter, the "West Davis Highway" got adapted into today's Legacy Parkway, and there is no equivalent at all to the modern Mountain View Corridor...)