Leaving aside the dishonesty in the campaign voters were given a binary choice but no idea what voting leave would actually mean. There are a number of different ways to leave the EU ranging from no deal to a Norway model. All May offered was brexit means brexit. She then proceeded to shoot herself in the foot by laying down her red lines to humour the hard core brexiteers. She followed this up by shooting herself in the other foot with her disastrous election campaign.
She then negotiated a deal which pleased nobody and keeps expecting parliament to approve it. The deal sucks and everybody knows it. Even she admitted that it was worse than remaining in the EU!
So what are MPs supposed to do? Back a toxic deal?