Because the cam is too big for the static compression. People too many times do not calculate the dynamic/cranking psi when deciding a cam and end up with less than optimal throttle response at low speeds and timing so high they may as well lock it out at full advance.
Ideally you wanna shoot for an 8.1- or better dynamic but depending on the chamber and head material try and keep at or below 8.5- 170'ish psi dynamic...however if you are experienced in tuning and building, you can run it higher like I do at 8.8 dynamic-185psi
In the future....don't stop thinking after the 10.1 compression pistons go in that its good , think about that cams intake closing, run it on a calculator , cause if you don't...you are building a dog and leaving yourself short on torque.
