You are not absolutely wrong - just mostly.
I agree with you that there is another factor '............she has nothing to gain and everything to lose....' as you say. So it may well be true that if this was 'just another election' and did not have the Brexit factor at it's heart, May, or any other sitting PM might wish to avoid debates.
But this is a side issue and the point I make about the negotiations is absolute fact - and should easily be understood if people just take time to think.
E.g.
"Mrs May - can you absolutely confirm that once the deal is concluded the UK will not be making significant contributions to the EU?" or
"Mrs May - following conclusion of the deal can you confirm that there will be no areas of UK life that will be subject to the jurisdiction of the ECJ?"
"Mrs May - can you confirm that you would be willing to pay money into the EU if it was to secure access to the single market whilst not being forced to accept FOM?"
and many many more such questions.
There are 3 stakeholder groups that would wish to hear the head of the UK Negotiating team expose key aspects of the negotiating strategy, her Red Lines and leave herself tied to 'hostages to fortune'.
1. the EU Negotiating Team - very useful information which will give them the ability to play games with the UK to back us into corners where public commitments have been made.
2. The Remainers - largely for the same reason, but for a different target - they want to undermine and hopefully reverse Brexit. They would wish to keep in the public mind a bunch of doom and gloom and if told a number of the key deliverables from Brexit they will be all over the media explaining how they cannot be achieved - how they evidence some back-sliding etc. They will essentially be agents of the EU causing major distraction. May will want all this to go quiet and following A50 issue it is starting to transfer to smouldering rather than an inferno - why would she pour petrol on it?
3. The Hard Brexit cadre - that will equally want to jump on anything they perceive to be a reduction from the 'fullest Brexit'. May might well have to make compromises as the negotiations unfold - that is how negotiations work.
May needs to be unfettered by all 3 of these groups as she goes into the negotiations - that is why the election is an excellent move. With a large majority she will certainly be free of the Hard Brexiteers threat, she will also be able to face down a lot of the Remainer noise as it reduces. Most importantly it will remove from the EU the hope that they have hitherto had good reason to hold that machinations in the UK can lead to Brexit being undermined from within. That means that they will have to face up to the fact that we are leaving and get down to negotiating rather than stalling and dragging things out.
