What i think out weighs everything else on this matter is Vito had no need for the drug business,
That's why I think Solozzo contacted Barzini before he went to Vito:
Sol needed a partner to give him working capital, police/political protection and affiliation with a major NYC family. But he also had something to give: the money his partner would make with him through drugs would buy power. Vito had all the things he needed. But Vito was already on top with businesses that weren't as risky as Sol's. He didn't need Sol's money, and the dangers associated with it.
So Sol must have chosen Barzini first--he was impatient to succeed Vito as No. 1, was younger and more ambitious than the other Dons. Barzini told him that his logic was correct, but he still needed Vito's police/political protection. If Vito knows I'm your partner, he'd say no--he wouldn't want his capital and police/political protection to make his chief rival stronger. Go to Tattaglia. He's a pimp--Vito's not worried about him. Tell Tatt and Vito anything you want, but I'll be your silent partner."
