We use all the development time we have. If we provided it a few weeks in advance it would change pretty drastically by the time it was live and wouldn't be much benefit for planning.
This thread was added on June 07, 2020, with posts from Bex_GGG.
Original Post
https://www.reddit.com/r/pathofexile/comments/gy1vc1/is_there_a_good_reason_why_we_only_get_the_new/