They considered him to play Riker btw

I mean, I've never seen Jeff's audition for Riker. I'm sure he was great. He's super talented. That said, Jeff doesn't have the physicality of Frakes. I think Frakes is literally 6" taller, broader shoulders, all that stuff. Frakes is definitely more of a traditional cowboy hero-type. Jeff wouldn't have brought that physical presence. With Jeff, Riker physically would have been less Gary Cooper and more Alan Ladd, to extend the cowboy metaphor.

I also think casting Jeff would have made Riker more cerebral and probably a bit less friendly. Jeff, to me, has a certain fastidiousness that comes through in all his roles. He feels more mental, more critical, more intense to me. Played by Jeff, Riker would've definitely evolved into a different character, the same way Sisko would've been a different character if he'd been played by Sid.

And of course, we'd have been robbed of Jeff's brilliant turns as Brunt and Weyoun (and Shran too) which would have been a tragedy. So I'm glad things worked out the way they did, even if Jeff's bank account might not agree.