Yeah I can see that especially when they have releases where the mono is in one channel where others will have it two channel.
dual mono/regular mono won’t make a difference either if there is hiss and bass reduction involved, sometimes in cases (like with The Godfather) a lossy dual mono track will sound better than a lossless 5.1 track due to lack of hiss or bass reduction on the lossy mono track unlike the 5.1 where there was bass/hiss reduction applied