Well it's just my opinion, but I recon Pep gave Maffeo a fair old looking at, & decided he wasn't good enough as a footballer.
I thought he should have been a first team squad player for several years (what we had ahead of him, was just not that good, full stop) but I recon Pep tested him as a wingback, to see what he offered on the ball & he basically offered nothing, so he sent him away.
We haven't seen him since & imo, he's on trial now at Girona, to see if he is good enough creatively, & I have to say, even as a committed believer in playing young players, it's madness saying he's currently better than Danillo.