I live next to this coal mine and the wind farm is on my monthly Autobahn trip right next to me. Maybe to shed some light on the "why":

The coal mine was scheduled to be mined until 2038. The plan was to extend the mine to the west, the wind farm is to the east of the coal mine. RWE of course has big investments into mining this lignite until the very last possible day. There are problems with extending to the west though: old towns still exist there and the residents would of course love to stay in their homes the family had for generations. To the east, where the wind farm is, there is nothing but fields and some wind turbines. There are about 150 turbines in the wind farm and ~15 of them are standing where the mine is extending to now. Those 15 also were the first to be built for the wind farm and they are nearly at the end of their lifespan, some of them are even deemed structurally unsafe.

Of course it would be better to stop mining the lignite but decades ago the contracts with RWE were made and just forcing a company out of a contract that is worth billions of Euros is extremely bad precedent and would hinder future investions. Buying out the contract to cease mining faster also was not possible, because RWE was unwilling to settle for a reasonable sum of money.