Oh, yes! Lucas, anyone? But, with Spielberg he still manages to make watchable and reasonably enjoyable movies. Not up to par with his classics, but not bad either.
I think the creative well runs dry and you eventually begin to reference yourself in your own work. I compare Spielberg and my guitar idol, Eddie Van Halen. Both hit in the same decade. Kinda came outta nowhere doing things nobody had ever seen before and each new work blew minds for over a decade. Then, the bag of new tricks runs dry and they coast for a bit, still producing solid work but carried largely by the legend of past glories.
I remember seeing Tin Tin and enjoying it. But, I could also see where so many moments and sequences were lifted from his earlier movies, almost shot for shot. I do the same thing with Eddie. I listen to his "more recent" work and can hear licks and such lifted from earlier songs. Hey, they're his to lift. But, it saddens you a bit to realize the well has run dry. The old bag of tricks can only entertain us for so long before what was once revolutionary becomes, "seen it, heard it" and we're left unsatisfied wondering if the master has lost his touch. In the case of music, Ed will always impress with his ability and live work. People will always cheer, "Eruption". But, Spielberg can't fall back on doing Jaws or Raiders or E.T. or Close Encounters to please the crowds once again.