I agree with what you said about certain manga having appeal despite not being masterpieces.
It's a lot like movies and TV series to me. There's certain movies and TV series that I enjoy watching, but would never pay to own the DVD or Blu-Ray of.
That's not to say these productions hold no entertainment value to me, it's just simply that they have a baseline entertainment value.
In the past, before streaming services were everywhere, I would sometimes end up buying something out of the $5 movie bin just to watch it. Or I might find something for even less, like the budget $1 DVDs they used to have everywhere. I'd buy something just because it looked interesting, and I'd take a chance on it and see if it's any good. I'd also use rental stores or DVD-by-mail services, but there weren't nearly as much available in those stores as there are on streaming services nowadays, so it caused me to also look in cheap movie bins for interesting stuff.
Now, with the prevalence of streaming, though, I'm much more selective of what I purchase. If I own something nowadays, it's because I genuinely want to own it. I want to keep it so I can watch it over and over, and also to support the artists that made it, because I want to see more stuff like it being released. This isn't true of works with that baseline entertainment value. For me to want to own something, it has to go beyond that baseline value, and it's as true in the manga world as it is for any other form of entertainment.