The dose for prevention is a fraction of the dose for people already infected. Maybe per year? I don't know, I don't recall the details, but even so that's without the economies of scale that would intervene if it was a worldwide effort.

Re: vaccines, JP Morgan estimated Pfizer alone will make $100B from vaccines. I don't think manufacturing Ivermectin is complex enough that it would net ANY profit, the effort would be organized completely differently.

Lastly, I don't think this is a conspiracy, either for money or politics, going for vaccines was just the easiest sell for both people and governments, and doing anything different would have been extremely difficult (see Sweden and lockdown policies).