The way to foster long-term brand loyalty amongst the most serious photographers is to get them to buy lots and lots of your high-end lenses. Sony has failed to do this because of their reluctance to make a very deep and diverse lineup of world-class native lenses for their full frame mirrorless system. The way they have positioned their product lineup in the marketplace, it will make it very easy for their mirrorless customers to jump ship once something better comes along.
Actually given that the FE mount is 3 years old, Sony has actually put together a pretty comprehensive lens line-up covering everything from the UWA focal lengths up to 300mm. The glaring omission is the super-telephoto stuff that sports and wildlife guys use, but it seems that they're targeting a very wide audience and the outlying excluded market is the sports and wildlife guys...probably because frankly, mirrorless AF hasn't up until recently up to the task of shooting sports and wildlife.
There definitely is an opportunity cost associated with Canikon not releasing a full-featured mirrorless body (sorry EOS-M5...you're still crippled compared to your competitors). Every year they stay out of the mirrorless market, Sony further cultivates this market for themselves...and anecdotally speaking, though most of us started with the intention of simply adapting Canon glass, I'd say the majority of Sony mirrorless shooters eventually switch to shooting native glass. (I no longer use any Canon glass myself).
But its a tough proposition for Canikon...a full-featured mirrorless body and corresponding lenses might allow them access to the one camera segment actually growing, but at the expense of cannibalizing sales from their bread and butter DSLR's. This is likely why Nikon ditched the DL. At an aggregate level across all product, given the cost of R&D, they could reasonably be in a worse position in the short-term.
Having worked in finance my entire professional career though, I've seen too many times where chasing financial performance in the short-term has set companies up for failure in the long-run. Very often its crucial to spend/lose money in the present to set yourself to succeed over the long-haul, because its very hard to catch up when the market has moved on without you. Opportunity cost is a real thing, but something rarely considered....