I've been suggesting that they make Thermal an unlockable module for a long time. But that only made the QQ patrol come out with arguments like, "why should I have to unlock a technology in 3050 when i have it on my car in 2013?"
Because game balance.
That's why.
It's pretty lame that the game is best played 80% of the time in thermal mode and that you can see mechs from across the entire map when using thermal. I hate the fact that you are willfully gimping yourself if you don't use thermal.