Mech disc brakes on road bikes

Yeah, it's basically down to inflation/brexit/exchange rates, £1000 is a key price point for a number of reasons and hydraulic road systems carry a hefty premium, and competition on price is limited to the big three, and campags entry level hydraulic potenza system costs nearly a grand just for the group.... and fundamentally mechanical disk brakes are still cheaper to make and supply.

On mountain bikes the brakes are usually a completely separate component to the gears, so there's much more competition on brake system pricing, plus obviously the market is much more mature, and it's easier to make a lever that is just a brake lever and not a shifter too.

The closest thing to that competition you have is the old TRP parabox/hyrd brakes and the newer Giant Conduct, which for fairly obvious reasons you don't see on other company's bikes although is pretty cheap to retrofit yourself (if a pig to setup).

Still, with an eye for a bargain you can fairly easily build yourself a hydraulic road bike for under a grand, you can now find shimano hydraulic shifters & brakes for a couple of hundred quid, especially if you go back to the older systems, or if you get lucky you manage to pick up the R7020 groupset on wiggle for £350....

I've just gone hydro on the commute bike and had to put tyres on with a bit of grip as the old ones were easy to slide with TRP Hy:Rd callipers.