There are lots of answers I could give to this question, but I think the importance of defensive midfielders tends to be overemphasised, particularly in Britain. Culturally, we tend to respect those types of players because they're 'honest' and 'hard working', managers like them because they spend all week working on 'shape', and it's easier to coach defence than attack. But often, in my opinion, they are quite replaceable.
If you look at Man City, for example, they've been through Barry, Milner, de Jong, Toure, Rodwell, Garcia, Fernandinho, Fernando, Delph, Gundogan, Zinchenko in recent seasons, has it made any difference to their team? Fernandinho will go soon, and they'll just bring another defensive midfielder in, and you won't even notice any difference. Toure, albeit he used to get forward, was supposed to be irreplaceable, now he's long gone and they're better than ever.
Also, there seems to be this odd phenomenon where some defensive midfielders gain acceptance, and then they're beyond criticism, but others are continually attacked. Kante would be a good example of one beyond criticism now, and Makelele from the past. But then Chelsea fans constantly ridicule Jorginho because he 'doesn't do anything' (neither does Kante, if you want to base it on goals and assists). Xhaka is constantly derided by Arsenal fans. Henderson was slagged off for ages - now he's playing a bit further forward, and 'doing more', so people have decided that he's a good player now. Milner would be another one from Liverpool, who has been accused of not 'doing anything'.
I think often DMs can look great in a strong side, but then you see how limited they are when they move elsewhere. Nicky Butt would be one who has 15 medals, but after he left United racked up around 220 appearances, yet never again had any relevance as a footballer. So I can to some extent understand why fans think Jorginho doesn't do anything, but I think players such as Kante, Fernandinho and Makelele are overrated in terms of their contribution to the team. For example, Fernandinho missed most of the run in for Man City. What was the result? They won every single game without him.