you just happened to catch this particular one, otherwise it has been happening for months. the spike size has also been the same size pushing the mempool to about 10-15 MB and drive fees up to 20 to 30 satoshi/bytes. this is one of the problems of adoption growing faster than scaling.

as for the fees of these transactions being low, the reason is because people know nowadays their low fee txs (like 1 s/b) will go through fast enough. for example during spike of today it would have taken a 1 s/b tx 12 hours to confirm in worst case scenario