Because he didn’t want to get arrested for assault.
Jesse’s a punk and a poser. He was never a “Navy SEAL”, he was a “Navy UDT”. The SEALs didn’t exist until after Jesse left the Navy.
Jesse Ventura was a UDT and the closest James Janos (his real name) got to Viet Nam was an Olongapo, Philippines cat house.
Correction: at the time Jesse was in the Navy (1969-1975), both UDT and SEAL designators were active; UDT was combined with SEAL until after Jesse’s enlistment was long over (1983). If I was Jesse, I would not want Chris Kyle to get p.o.’ed at me for a very good reason . . . my body staying above room temperature.