It seems to me that the logical thing to do as a Pharaoh would be to try and build the larger pyramid ever, but they didn't. I can't understand why, especially since one of them comes really close, so it looks like a conscious decision: https://upload.wikimedia.org/wikipedia/commons/9/94/Giza-pyramids.JPG
Was surpassing the older one a taboo?
Mortuary temples did not necessarily get smaller, but rather changed. They went from mastaba-like structures and shifted during the architectural reign of Djoser to step pyramids. During the Ramassid period, Ramses II built a massive mortuary complex. The temple of Karnak and Hatshepsut’s mortuary structure are also massive complexes that definitely rival Khufu’s Old Kingdom period complex.
For sources I would check out Marc Van De Meiroop’s covering of Egypt in “A history of Ancient Egypt.” (But I’m pretty biased towards Van De Meiroop’s work)