1st summon attempt (when yuji at the finger): jujutsu satan literally just reincarnated, only people who could take him on are special grades/ SOME (or none) grade 1s
2nd attempt (Shibuya incident, when haruta pulled up): basically exhausted from toji and dagons domain, then jumped (by haruta). he probably hoped mahoraga would immediately go for sukuna after haruta died (or sukuna noticed maharaga)
3rd attempt (when sukuna activated the binding vow with yuji): sukuna knocked out angel (which somehow didn't break the condition of the binding vow), which left megumi alone, then he tried to summon maharaga (which was basically the only thing that could deal with/stall sukuna), but the handsign was interrupted by sukuna
all were valid