Re: It's a con
No they don't - there are ISPs that don't use an Openreach last mile. BBrn, gigaclear, fibrecity.
But none of those allow other CPs to use their cables so the only thing you can do is switch back to an Openreach based solution. The ones you list are mostly present in areas where they offer a far better connection than openreach so it's not much of a choice.
If you're in a big city, KCOM, Colt and Verizon will lay a fibre to your door.
Eh? KCOM are rolling out fibre everywhere they cover (Hull and environs) but I don't think they operate anywhere else. Do Colt and Verizon actually lay any local loop cable in the UK? I'd be moderately surprised. I thought only openreach and VM laid local loop in the UK.