With film you have to supplement a lot of what's achievable in digital via guessing and checking with careful thought. You also have many fewer opportunities to get the shot right before you exhaust your film and probably blow the moment replacing it.
This makes film into a forcing function to perform excellent technique and to pre-visualize your shot. This creates better technique.
It's also nice that film has a very high effective resolution (when drum scanned), that film grain is a favorable aesthetic right now (it was usually considered ugly before digital), and that film has a logarithmic response to light meaning that it can handle a wider dynamic range than digital.