Most obviously, because of electoral maths. The current result increases the risk of a messy hard Brexit, especially as most of the Tories that lost their seats were moderates. May is going to require the support of her hardest Brexit supporting mps to get anything done, so while voting against the conservatives may feel better, the outcome is going to be worse than if, on a case by case basis, those wanting a softer Brexit had supported Tories where they stood. Corbyn never stood a chance of a majority government.
I voted remain, but we lost the referendum. I don't support a rerun as part of the negotiation, because it massively weakens our negotiating position. Likewise I don't support the idea that the government should ignore the referendum and remain in the eu. In order to move forward, we need to negotiate a good leaving deal. That required strength and realism, and now we don't have either.
The election made a hard Brexit (or a complete breakdown in negotiations) more likely than it was before, and that is the fault of the electorate, because the electorate are the only people responsible for their voting choices.