The obvious counter position would be that if you didn’t want to leave the EU you shouldn’t have triggered article 50.
You can see the EU position. They have to spend a lot of expense negotiating when it is triggered. If it can then be revoked unilaterally it holds no real weight. Countries can use it at a whim as a negotiating tactic, holding the rest of the EU to ransom.
My opinion is that the triggering was the act of leaving and the two years was a chance to get things in place for that. The triggering was not a suggestion that the UK may or may not leave, depending on how it feels that week.
It does make sense that it could be revoked with good will on both sides but to be able to do it unilaterally messes everyone else about.
However, I am not a judge in the European Court so who knows how it will go down.