Once again, apples and oranges. At the end of the day, LoL isn't Runescape. The regular game, in spite of all the complaints, is still unbelievably successful. Runescape alienated players by removing entire areas of the game; that'd be like if Riot made SR 4v4 and removed jungle monsters, smite, and jungle items. Thus far, Riot has only made certain roles better or worse. Whether certain roles are unplayable is a matter of opinion, rather than something that was factually removed the game.
Besides, you're missing the point; it's too much effort that could be put towards doing stuff for the modern game which, as I said, is still insanely successful. If it ain't broke, don't fix it. I that probably sounds idiotic from the way people are talking about the game, but think about it from a business perspective: Why would they unnecessarily spend major amounts of time and money on bringing back old League (which might not even be as good as people seem to remember, plus you have to factor in all the newbies who would probably either love it, hate it, or be indifferent) when the game they have is already making them plenty? Why not invest all that money into increasing and insuring that success? It makes no logistical sense to take such a big gamble.