I can think of many reasons.
1st - Konami and Sony restrictions on editing, always hiding, locking or removing features game after game, instead of adding new ones. For example, Konami kit limit, removing teams from other european that were so useful for editing, removing stadium editor, etc... Also I think the chants can't be added because of Sony restrictions. As I am tired of saying, PES has the potential to become the best football game ever, much better than FIFA, with a much smaller budget. Forget about licenses, there's no point at all on paying thousands and thousands of dollars to get Borussia Dortmund license if they can't get Bundesliga, same for At. Madrid, Barcelona, Liverpool, Arsenal - Why paying thousands of dollars to get those if they can't get license for Premier League/La Liga? They're making the wrong moves. Save money on that stuff and invest it in other ways to improve their game, such as paying for more employees to make more 'fake' leagues, so we can add the ones we want to play with.
2nd - PES 2018 was a deception for many people. Some didn't enjoy the gameplay, others say it's no different from PES 2017, and they won't buy the same game again (at least, those are smarter than most FIFA players, who keep buying the same game year after year...). The hype is gone.
3rd - Most people play always the same leagues - Bundesliga, MLS/Liga MX, and CSL/J-League. And all of these were already done, so there's no need to do anything else. Then, they play Master League until they are bored and leave the game forever. They only care about filling up the fake team slots, and never think on all the possibilities that they have if they invest some time on the editing menus. That's it. This isn't my case, I love playing with new and different teams and leagues.
4th - The focus on MyClub and online modes. I already tried MyClub, and I must say, for me, it looks like a cheap copy of FIFA's Ultimate Team. Ok, some people like to play it, there's no problem, just because I don't like it that doesn't mean other people don't enjoy it. But MyClub is taking the spotlight and leaving ML/BAL behind. And MyClub is all about those big players that are already in game, so, there's no need at all for editing to play MyClub.
5th - People that steal option files. Like [MENTION=70077]rogers150862[/MENTION] mentioned above, OF makers feel very bad when they see their hard work that they shared for free being sell by other people online. Or even if they aren't selling it, sometimes, they share it and put adlinks, making money from other people's work. That already happened with me: I once found some of my kits on pes-patch website with an adlink. I complained and the uploader added a direct link for it. And I must say, admins here don't seem to care (sorry
). There was a guy here (@ashrafyoussef) that posted a lot of other people OF's with adlinks. The account wasn't banned and his posts are still up. I can't see how a community is supposed to work like this.
In my opinion, what we really need now, besides more attention from Konami, is some editors that bring us new and different stuff, so we can get back the fun that PES once had, basically, someone that give this game a second life. On PES 2017, for example, I made some contribution to the "All National Team" OF. That was a really unique project, something that I have never seen in PES before: All the national teams of the world, recreated with great accuracy, on PES 2017 for PS4, all made by a small team of passionate players - it took 9 months to do, and hopefully it will still receive some updates and new teams. Same for Ratmundo's classic option file, or the other people that did lots of classic club teams. They attracted (and still attract) lots of people. Things like this should be an example for Konami, how they would get more customers. It would be good for both sides - for the players and for their pockets.
I am still and editor, I will keep customizing the game to my liking, no matter what. Even if I had to edit all by myself, I'd do it, I am not afraid of hard work. The only thing that keep me from editing more is lack of time due to other things in my life.