Yep, unions are currently working for those goals too (fight for $15, etc). But it’s one of those areas where the core of a union as a collective bargaining entity is also eroded by having to divert all their energy into fighting for the basic landscape of labour rights. If your union is spending all those dues on fighting to get the ground floor of universal rights locked in, there’s not the bandwidth left for doing the work of being reactive and doing the specific work of making sure office X is providing the environment the workers in that office need.
The other point on this is that those protections being eroded happens in the political sphere, where the removing of union protections also happens (in removing the right to strike etc). So you can have the very best union in the world but if you aren’t also directly pushing and electing politicians to solidify pro-union legal frameworks then you’ll just end up being part of an illegal union with no power (and funds seized by the state). Without the politicians working for the people, the unions can’t work. Without the basic labour rights being universalised and solid, the unions can’t work for the actual job of collective bargaining that represents the specific needs of the workers in that union (which gets into the podcast discussion about unions that can feel like a bad deal for workers - also something Patrick has talked about on previous shows about his first union job and getting basically nothing except losing the dues while working retail). Your politicians need to be this good on labour rights for unions to really shine and fixing politicians means voting the bad ones out/becoming activist citizens.
The US seems very active in directly pushing representatives, except when it comes to labour rights and then it seems to be the expectation that you mainly look to pay a union to act as a lobby for your basic rights (while living somewhere that is extremely lacking in those rights compared to elsewhere - possibly a sign that the current system is not a great way of doing things). Unless you’re not able to unionise etc. Maybe it’s not that unusual (eg not agitating for certain things but paying the ACLU a donation and leaving them to work on your behalf) but it often looks, from the outside, to be particularly skewed.