Then you have an imperfect understanding of exactly how much damage you're getting from your DoTs. If you don't let your DoT fully tick and drop off, that means it did not do its maximum damage. Overwriting a DoT means eating whatever ticks it had left, effectively having them go to waste.
For example, Demolish does more damage than Snap Punch if it fully ticks for the entire 18s duration. However, if you were able to overwrite it so that even a single tick was lost, it becomes a total less damage than Snap Punch... at which point why even bother with an attack that spreads your damage over time when the other choice does both more total damage and does it instantly?
Overwriting DoTs is bad. You do not want to do that. The game currently prevents you from overwriting an existing DoT if it was placed with more buffs before - basically you can only overwrite your DoT with a stronger one, but a weaker one will fail and not go through.
Get out of the mentality that 1-2s of no DoT uptime is bad DPS. It isn't. What matters is letting your DoTs fully tick until they are complete, and then applying them again as soon as possible.
