@MsYutani [nb, opinions ahead] The next GE wasn't due for another 3 years or so. Currently the Tories don't have much of a majority, parliament (and the country) are somewhat emboldened to speak out about Mays overreach and broken promises ATM. Part of the rationale will be that right now the Torys core supporters will be very Pro May as she has triggered article 50, whilst her detractors are not unified into supporting one party & not especially organised.

If she gets elected now her Brexit strategy is legitimise by association and she has a swift soundbite to offer her critics -"I won the election"

Also, May<3Thatcher