More specifically they don't understand the customer. TT gamers who are passionate about the industry WANT to create their own content.
Gamers that want to create their own content are not the primary customers of Hasbro. This has been true since the beginning. The entire RPG industry is built upon selling rules, settings, and adventures. Three things that players could create themselves.
Trying to build a business selling products to people that don't need them will never be a success. I can't blame Hasbro for marketing their products to the people that actually purchase products.
What you’re selling is Convenience/Time Saving.
Sure, you can build a bespoke ruleset and try and balance it yourself over the course of weeks or months -or- you can buy this pre-built system and tweak it a little and be able to play in a couple hours.
Sure, you can build your own monsters from scratch at a cost of hours per session to prep them -or- you can buy this book filled with hundreds of monsters to cover everything you’d need.
Sure, you can design your own setting from scratch and fill it with unique NPCs and adventure hooks taking you hours or days of effort -or- you can buy this setting book that’s done all that work for you.
Sure, you can make your own adventures and maps, but sometimes you just don’t have time or are looking for inspiration.
People make billions providing customers with things they could, in theory, do for themselves. The value is in allowing people to skip the things they don’t really want to do so they can get to the things they do.