In a traditional 'desktop style' app simply ported to the web this may be possible. But in a multi-user app that may not be the case.

What if the record you deleted was subject to some kind of uniqueness constraint. If another user has added a record that has the same data, then flipping the delete flag off again would not violate that constraint.

Sure, it could be handled by checking if the constraint is violated. but you rapidly run into a lot of code to implement that one feature and dealing with thinking of and testing all the edge conditions makes it much easier (& cheaper) to focus on other features.