Huge Rush & Geddy fan here. And I'm about to type something that makes tons of sense, and others might have thought, but not admitted or spoken aloud.
So, in his 40+ years with Rush, Geddy's been primarily associated with Precisions ( early on ) , Rickenbackers, Jazz, Steinberger, Wal, then back to Jazz.
And since none of us are getting any younger, and number of viable years for income is diminishing, economic viability has to be a consideration.
Fender, being the biggest fish in a relatively small pond, makes the most sense. They've had a Geddy Lee signature Jazz for years already, at a reasonable price point, then upped the ante with custom shop and USA versions. Win for Fender, win for the esteemed Mr. Weinrib.
You think Rickenbacker, Wal, and / or Gibson-Steinberger / NS Design could offer Geddy what he needed---in the studio, on tour, or his bank account---let alone meet the demands, at the requisite price point(s) for themselves for a marquee rostered endorser?
I don't blame Geddy in the least. It's a numbers game, and looking out for one's best interest, economically as well as in the interest of history, reputation, and the fullness of time, the Jazz is a logical, easy choice.
Go ahead, call me every name but a child of God...search your feelings, Luke...you know it to be true.
Plus, when you get down to it, Steinbergers are essentially composite headless dual split coil precision basses. The pickups look like humbuckers on the outside, but are split Ps behind the scenes.