Exactly.
And it's not even that the pentaprism (or pentamirror in cheap cameras), mirror, and dedicated AF module is that expensive, it's that it's a mechanical system that must be calibrated precisely, especially in higher end cameras that tend to use faster glass. The reason Nikon and Canon never release any really fast consumer glass is tat on the cameras they were paired with, they just didn't have that sort of tight tolerance.
One of the more interesting changes Nikon made that will probably pay off long term but definitely hasn't yet today just because of the low volume, is tighten the sensor mount tolerances in component manufacture, so they no longer need to shim the sensor during assembly. The ultra fine adjustment is done by adding a register distance correction to the IBIS system. Sony and Canon still shim the sensor for now, but knowing how Japanese companies try to work together they will probably switch over to the Nikon system in the next few years. The Z mount lenses also use the Canon system of thinner/thicker mounts, rather than the F mount system of shims, and Canon, Nikon and Sony all use lenses that focus past infinity at all temperatures so that the register distance on the lens isn't non and Nikon haven't fleshed out their lineups yet: Nikon needs pro glass and APS-C, and Canon needs decent bodies, consumer glass, and to pick a mount, and Sony needs a competent UI designer, better build quality, and feature completeness (getting an intervalometer just last month via firmware is pretty boneheaded). The only people with a clear path to move out of DSLR right now are 6D, D610, D750, D800 and D810, who should move to the EOS R/RP or Z6/Z7. On the flipside, unless you need something photographically in the next couple of years or your body is dead/problematic, there's little reason to buy a DSLR right now with mirrorless models coming down the pipe. The only exceptions I see to this are weird bodies like the Df or F6, but those are hardly mainstream.
300 f/4E, 500 f/5.6E and 200-500 f/5.6E. Fuji just makes good bodies that make ergonomic and feature sense and there isn't a dud lens in their lineup, which is the best around for an APS-C sensor. Sadly they're not involved in this big sale, but the reasons I've just stated are probably why.