Plenty of people have been offered lower APRs but you have to remember Monzo want to make money so it’s in their best interests to offer the higher APR to people.
Try another bank if you want a lower APR, keep checking back with Monzo and wait for the APR offer to drop a bit.
I think that Monzo are more risk averse at the moment.
The people on 19.9% likely accepted that offer when Monzo were being less risk averse (pre-covid)
I just got a £15,000 loan (house redevelopment) yesterday from a high street bank with a good APR. Monzo won’t even take a look at giving me one. Monzo are very very cautious in lending. It’s something you just need to live with unfortunately.