He hasn't hit his ceiling yet
Lauri Markkanen is just beginning to hit his prime, and still growing into a complete basketball player. He is younger than Jokic and Porzingis and doesn't have the talent around him that those guys do. His offensive efficiency stats are the highest they've ever been over the last 2 years, and that's with him being the only true offensive threat the Jazz have night in and night out.
The Jazz have been pretty quiet this free agency, and if they want to keep Lauri, they need to capitalize on his prime, and go get him a supporting cast, to open their championship window.