They do, albeit it's a slow process:

- https://en.wikipedia.org/wiki/Pfizergate

- https://www.independent.co.uk/news/world/europe/eu-secret-gr...

Ironically, those are two separate cases of one high-profile EU politician (in fact, the very head of the same parliament that pushes for mass scanning of private messages) BOTH involving secret text messages that the mentioned politician refuses to reveal.