Almost everyone I know only buys games during the big seasonal Steam sales, perhaps with the exception of the occasional “must have.” By not allowing resales, game developers are forced to offer big discounts during these sales in order to capture the “clearance bin” prices that would otherwise go to the secondary market. If reselling were possible, game publishers would never offer those discounts since resellers would always undercut them.

I have personally purchased some Steam bundles that included games I’m actually interested in playing for less than a dollar.

It's easy create a "tax" that goes to the devs for every resell. Actually that would be better than the old physical games reselling.

If forced Steam will surely put a "tax" for themselves, so why not add the devs.