Conspiracy theory: May expects the Art 50 talks to not go well and having the election after Brexit has fully played out over the next two years will damage her

Conspiracy theory: May expects the Art 50 talks to not go well and having the election after Brexit has fully played out over the next two years will damage her approval rate. Having the election now means she doesn't have to worry about her approval throughout the negotiations and won't have to face an election right at the time the consequences of Brexit are felt by most voters.