One difference is that, as Bluetooth demonstrates, frequency hopping can be extremely fast at basically no cost. If you have a broad enough spectrum that the attacker needs to cover, that actually makes it harder to eavesdrop by adding a real cost (either a better listener or more listening devices). TOTP, on the other hand, typically allows for many seconds of leeway between the two systems, since there is no direct radio communication between the two systems that they can use to synchronize clocks (in the sense of a clock signal rather than actual timekeeping devices).