I don't understand why they don't just vote to cancel Brexit.
The Tories are the one who promised to allow a referendum and follow the results, they can't really pull this off, especially since they claimed Labour would ignore any results and do as they wished. That's why they're endlessly trying to delay the thing, they need to bump their margins back up so they can try and survive an election post going back on it.
Arguably holding another referendum on some kind of shitty "plan" is the best way out, but they're scared to death it will pass and they'll be double locked in.
Labour should by all accounts be dead in the water from shooting themselves in the foot constantly, but the Tories saw THAT as a challenge.