For us this problem pre-dates the pandemic. We also used to travel without reservations except for popular destinations like Yosemite, Yellowstone, Zion, etc. No more. Now I have reservations for virtually every night of our upcoming five-week trip to Oregon. The only reservations I didn't do this time was for heading out and back, but since it's across NV and UT, we know of boondocking sites in the middle of nowhere where we can stop (we will travel on weekdays.)
Even for a one-week trip here in CO, I had reservations as soon as they opened up. Now we will do some camping this summer at NFS CG's that don't have reservations, but we will arrive early in the day on a Monday through Wednesday.
As a side note, we now camp a lot of NFS CG's in areas where we used to do a lot of boondocking. But there are so many people boondocking, we're willing to pay for a NFS campsite just to have a little more privacy. Some popular boondocking locations are so crowded they are like parking lots.
I hate the lack of spontaneity, but have learned to adapt. I especially feel sorry for people who work in jobs where they can't request time off very far in advance. Don't know how they fare with the need to reserve so far our.