What's the differences between these two guns...and why did the 700 become so much more popular?

The actions are pretty much identical except for the trigger system where there are very minor differances. The Model 7 basically has a compact stock and shorter feather weight barrel on it.

It's just a compact version of the 700 and came later than the 700 which is why the 700 is more popular. There are not as many people that want a compact, light weight rifle as there are that want a 'standard' size rifle.

I think the 700 beens offered in a ton more calibers then the 7 ever has also. Theres only a few versions of the Model 7 like youth, laminated and synthetic stainless or a regular walnut. The 700 been offered in every combo under the sun except for pink and purple pooka dotted(the next years classic).