I'm not sure that's comparable or even true. No other proprietary engine has as even remotely comparable market share in the freemium/Ad/IAP-funded/shovelware mobile game market.
Also Epic isn't trying to pay for 8000 employees (especially not just with their engine revenue) or service billion in debt accrued from (possibly unnecessary) acquisitions. It feels to me that Unity pushed themselves into a corner by increasing and don't really have any choices but to try and maximize their revenue any way they can.
e.g. Epic seems to have about 4000 employees and compared to Fortnite Unreal seems to almost be just a side gig for them.
Also let's be fair a 5% royalty would be much more likely to scare off their best paying customers. And looking at their current leadership and overall philosophy I find it easy to understand why they might not care that much what will happen to some indy/small developers who can't afford/don't want to pay for Pro or have more than 1 million users but can't generate more than ~$0.2 - 0.5 in profit per install.