I feel that some big name studios who made some excellent works that brought them a lot of money have definitely dropped down in the quality of their animated films. For example: Illumination Studios - who soared thanks to the success of Despicable Me, which already had an interesting concept: A villain who couldn't be a villain right and has to look after children he never wanted to care or love. The Minions had a very similar effect to the Rabbids of the Rayman series, and eventually overtook the main of Despicable Me in their own film. Now, with their 'Secret Life of Pets,' it's essentially a less than original version of Toy Story with animals. Not to mention that the 'rabbit' character we see seems to me a very crass 'Take that' at Judy Hopps - and not to mention that one scene I won't say but it isn't funny to a more mature film goer. Not to mention that rabid fanboy of a Minion who squeals at seeing Illumination Studios in the trailer. That just becomes ear-grating after a while.
I certainly expected that sequelitis would be set on 'collision course' for Ice Age after the series continued beyond 3. If anything - unless your confident that you can try to maintain a consistent level of quality or add to it, one should probably not go for much longer than a trilogy or so in my eyes. To me, I'd say Ice Age finished with the third film. There could have been stuff done to keep the franchise fresh, such as a new generation of characters, or maybe finish there at the end of 3, but it seems like it's just a cash grab.