I think its more based on economics. If Metro Exodus sells poorly on the PC then he believes that it would mean Metro 4 (or whatever) is then less likely to have a PC version. The lost profit arguement you use only works if the game actually turns a profit on the platform. If a potential boycott causes a loss then that's what they have to go off.
Honestly, I really don't get the fuss about Metro not being on Steam. Epic will be creamed if they didn't invest in their store when they're up against a competitor as dominant as Steam. Microsoft did the same in the early days of the 360 to try to syphon off some of the PlayStation base.
As has been stated, the issue isn't simply that Metro won't be on Steam for a year. It is that said deal happened just under three weeks from release. It is a bad precedent to set and it's good that people spoke up about it.
Regarding this latest statement, it is an easy way to lose a fanbase.
Exactly. If this had been announced months ago, a year would be preferable, then the outrage wouldn't be so heated. But, we are less than a month from release and they drop this bomb on people. Really, they should have let this release as is, but have a slight discount ($5-$10) on Epic Store to appeal to people. If they release another game, then they can announce this along with the game, or shortly after.