Think of it this way, if I took 1lb of air on the ground and put it into a box that box would have sides of x. As I go up x gets bigger because pressure is dropping with altitude so to get the same mass of air I need a bigger box. When you burn fuel you need a ratio of fuel to air that is determined by mass, not volume so I need to take that really big box at altitude and squeeze it down a lot to get the same density as at sea-level (and then squeeze it even more to get the right mixture in the combustion section). The thing is though, 'hot air rises' so just squeezing down to 1 atmosphere of pressure air at altitude is way hotter than the air on the ground and then you squeeze it even more to get it to the density you need for the engine and it is -really- hot. Engines are generally torque limited on the ground and TIT limited at altitude because as they go up you are power limited by TIT (turbine inlet temp, or some other temp limit related to the engine) because of this compression. Designing engines that can handle that massive heat and that massive force is really hard, but electric has the huge benefit of just needing to produce torque so it is way easier to build and can keep producing power at much higher altitudes. There are definitely challenges there, but they are likely much easier than solving both the heat and torque problems that jet engines have.
Duuuuuude, TIT is the temperature after combustion, not compression. Adiabatic compression isn't even close to the main contributor to TIT--heat input from burning fuel is. Also you may be confusing turbofans and turboshafts--helicopters have torque limits (not a helo guy, but my understanding is this is a gearbox or masthead structural limit rather than an engine limit), but if your turbofan can't hit RPM limits on the ground on a cool day you should seriously consider bringing it back for maintenance instead of going flying.
There are a lot of variations. I am most familiar with turbo props so shaft hp is the limiter on the ground and TIT is the limiter at altitude. TIT, of course, gets most of the heat from burning and I did mess up my explanation a bit. Sorry about that! You may be surprised how much of that TIT comes from compression though. The main point still stands, check the temp of that compressed air at sea level vs at altitude and for the same PSI out of the compressor you get a lot more heat at altitude. Either way though, the original point remains, electric has no TIT limit and you don't have to deal with 1000c materials spinning at 100k RPM so way simpler and easier to build something that keeps delivering thrust at extreme altitudes.
