Redrawing city boundaries is not exactly easy, mate!
Everything from road-works to Council Tax zoning would have to be changed!
You make it sound like a simple process, but it involves everything from sewage to City Governance -- same thing -- and there is NO WAY that Liverpool is going to undertake something so enormous, just to keep Everton playing within Liverpool city limits. Yes, the city does lose revenue from losing the blxxdy Blues, but the sheer, mind-boggling cost of moving the city-limits makes the loss seem trivial.
Y'know, if you thought about everything the City does... NHS Trusts, DWP zones, MPs, maintaining the buses and underground, roads, water-mains, power-grids, and so forth... you'd never have asked such a daft question. Those lines on the maps are not arbitrary, y'know.
That said... no effin' loss. Not an Everton follower. Give me our Reds any day!