For what it's worth, I'm an in vivo pharma researcher, and the standard is to not euthanize unless we need tissue. Unfortunately, I'd guess that 99% of the time, we need to collect blood, spleens, livers, etc. and doing so
reduces the number of animals needed in that study as well as the number of studies we run with animals. There are already a lot of pressures to keep animal numbers low, not least of which being that each of the cheapest mice is somewhere around $28 (you can see the prices yourself on their website, but I think my company gets some discount on those prices). Also, my time is valuable, and adding mice increases the amount of my time is spent working on that study.
I'm also on the IACUC for my company, and I can assure you that we do care about animal life. We go to great lengths to ensure that research is being done in ways that maximize animal welfare to the extent that is possible. The FDA requires animal studies for safety and efficacy, and we can debate the morality of testing in mice, then NHPs before humans, but the system as it exists prioritizes de-risking first human doses as much as possible. Given that system, it is the job of the IACUC to oversee and approve every procedure done to an animal in the facility or in our company's name at other facilities. It's a big job that, at least at my place, is taken very seriously by researchers and up the chain of management.