UEFA invites bids to host the CL and EL finals. The process is...something, but ultimately of the bids received, UEFA went with Baku. Keep in mind that cities bidding to host the Europa League final can't host a Champions League final, so cities like Madrid, Munich, Paris, London, etc. pass. However, the bid requirements to host the Champions League final are much more exhaustive which puts cities like Baku out of the running. I still argue that they should have a pool of 2-3 options and pick one once the group stage is over (ideally keeping it central to make it easier for fans of the teams to attend). Still have a neutral site, but if, say, Paris was the host city for the Champions League final and Lisbon for the Europa League, it would be easier travel.