You can only collude with someone you were in competition with. Shareholders of the same company by definition cannot collude with each other because they are not competing. Collusion would be Walmart and Target and Costco and Amazon unionizing together to negotiate wages.
Shareholder votes are public, but anonymous. The more typical scenario is that you hold on to the shares and create demand for the stock as a sign of your approval. Unless you own tens of thousands or more shares, you were probably not invited to the perfectly legal but private discussions about the proposals.
Shareholders recently voted against every single proposal that was also opposed by Amazon.[1]
[1] https://www.geekwire.com/2021/final-tally-amazon-shareholder...
I said "can openly" collude, not plain unadorned collude.
Amazon buys a competitor and suddenly what would be considered collusion prior is washed clean, because someone else could bid too? My whole point is how silly this transformation from illegal to legal is, if at the same time you want to prevent unions.
Unions BTW have similar restrictions to your second half of your comment (secondary strikes are illegal).