Why do we get 3* mods from the third tier mod challenge?

For the same reason we get 1 stun cuff piece per 100-150 energy, to make life miserable and convince you to spend money... Dont exactly need to be a scientist to answer this yourself m8 :)

I wouldn't care so much about the 3 dot mods if mods still had the 100% drop rate but it really blows when you sim 20 mod challenges and get zero 5 dot mods

To your other point I actually use lots of mods without speed secondaries usually because I need a certain primary and set bonus and haven't gotten one with a speed secondary

I use mods without speed secondaries on toons that don't need it. Typically tanks like RG or Shore.

My shore got one speed secondary on a protection primary but it was the last thing to show up so it's only like 4 and I was too lazy to do a new model so I just left it