F1 cars work on different materials, taking advantage of adhesion instead of friction to slow the vehicle down. Since they're going so fast and need to stop so often without a chance to cool down, they simply choose materials that work best consistently at the temps they're most frequently at. Same design concept is taken for things like super advanced jets, where they leak like crazy on the ground, but once at high altitude, functions optimally, due to thermal expansion.
As for Ti rotors and brake systems, there's no reason for friction not to happen, clamping onto it with a brake pad. The heat tends to go to and build-up at the most conductive parts first, which tends to be the brake pads. They recommend not using metallic pads, partially for this reason, as the pads transfer the heat to the brake fluid and that can cause issues like boiling any traces of water in the line (lower boiling point than the brake fluid), turning it into gas and creating the issues related to having air in the line and needing a bleed. Thermal conductivity shouldn't be a huge deal as heat from friction is deposited right where the friction happens; conductivity just spreads the heat throughout the rotor better, so there's no uneven hot spots.
Sometimes thermal conductivity is bad. There are cases in motos using 2 piece rotors with alloy carriers, with the alloy carriers conducting so much of the heat that it affects the grease in the hub bearings.
There's far more to consider than basic material science stats on different materials and choosing the right one. With enough forethought, engineering, and design, you can make things work with many different materials. For general consumers, is it wise to pay more for less, and for companies, can you make money through it? Some materials have other issues, such as ease to work with, brittleness or fatigue life, stiffness, expense, etc. For those that already have tooling for titanium, it wouldn't be too much extra work to make Ti into other products, without carrying over too much of the cost of the machinery to the cost of the product. If you already have tooling and know-how to work with steel...
There are already some Ti rotors out there and judging by those riding them, they are apprehensive about using them full time, probably due to the cost, but the Ti rotor users have a more positive impression of them over Alu rotors, at least between Carver Ti and Scrub Al rotors.