[ineedasername]

They've had 3 years, but not to act in the current (very different) circumstances than were present for that 3 year period. Most of that time was spent in the actual substantive negotiations, but those fell apart in their ability to gain parliamentary support, precisely because Theresa May held her cards too close to her vest and away from parliamentary scrutiny & input, and that gave rise to the time crunch here.

Regardless of whether they could have acted sooner, Johnson's move was to prevent them from acting now when faced with a new administration and new course of action that had every appearance of going against both the will of parliament and (though less legally relevant) the will of the people in that most do not support crashing out without a deal.

You can't claim they had 3 years to act on the current situation when the current situation just arose in the form of a new PM that was attempting to side step any parliamentary review or legislation over his course of action.

Finally, they actually did act this past spring to vote that no deal wasn't an acceptable outcome. It was part of a series of non-binding votes that established governmental norms should have meant that it would be honored. When, after Johnson became PM, it was clear that it would not be honored, parliament quickly acted in the short time before being proroqued to actually enact in law the requirement to ask the EU for an extension in the face of no-deal. So, not only is 3 years not what they had to address the current situation, to they extent that they could address the current situation, they did so. Their desire to do more was prohibited by Johnson's (now illegal) actions.