The way the timer works is that if someone takes a lot of time to pick a move, they have less time the next turn as you only gain 10 seconds per turn. If I wait until the final 5 seconds to pick my moves for example, I'll only have 15 seconds to pick a move the next turn; it doesn't reset as you're describing. It's still annoying to wait for the timer to go down the first time against someone malicious sure, but it's not sustainable for them. Some people really just do take a long time to consider all their options.
If you wanna look at how the timer works yourself, here's a
link.