They also had a long-planned, already-announced optional event that had a hard currency entry ticket price ($7.99 in the US), as opposed to costing in-game currency that players may already have had on hand (so every event ticket sold went directly into real revenue), and they didn't cancel the event.
Instead, they put a useful few things on crazy one-time sales (e.g. 100 Pokeballs for 1 coin, instead of 460 coins - but only one purchase per player), and, in particular, a similar sale on Incense, which allows you to summon Pokemon to your location to catch (so you can catch a bunch in your living room), as well as turning up the spawn rate everywhere, to make it _possible_ to do the event from your couch - normally the opposite of what they want for an event, but fitting with the times we find ourselves in now.
Also, the bits that they were nearly-giving-away wouldn't be enough to complete the event from your couch unless you were particularly lucky, but did generate a lot of good will in the community, so lots of players threw in some extra money to get the resources necessary to complete the tasks (to be clear, once you purchase the event ticket, you can complete it at your leisure - you could finish the tasks a year from now and still get the final prize - but most want to complete it right away).
(This is only the second such worldwide in-game paid event they've ever done - they've had yearly physical events at venues, like GoFest, but only these two paid virtual events that one could play anywhere.)
I'm not at all surprised that they raked in a bunch of money from all this.
(I have a Pokestop a couple hundred yards away from my front door - I have literally gone out for a few minutes each day for the past week to spin that stop to keep up my daily bonuses.)