They won't do it for a very long time because the Fantastic Beasts films are still coming out and the branding that comes from the OG films (merch, theme parks, studio tours etc) makes them so much money. Rebranding would take away interest and undermine that so it would be financially disadvantageous for JKR and Warner Brothers to do a remake, and they are the ones who hold all the rights.

On top of that there's still an enormous amount of love and nostalgia for the OG films. They are iconic and because of that they are untouchable. It's the same with the Lord of the Rings movies- although we are getting spin-offs we will possibly never see the main books remade on screen, at least not for a very long time.