Because a lot of it is believed to be a waste of time or something "silly" to worry about since it's been like that since the beginning of man (which is understandable in your mid-30s-50s, not your damn late teens-early 30s). We didn't get even hair loss treatments until about 30 years ago, and we assumed for 10+ years that they were doing the job on their own without realizing that it can lose efficiency over time and it becomes a hassle at a certain point, not to mention that there weren't even that many companies even involved in looking into hair loss until the late 2000s and 2010s.
Plus hair loss has had a stigma, but it didn't get severe until the social media age rolled in and now, nearly every young guy is worried about hair loss these days. Hell, even if you had hair and was only decent looking, it's tough getting with girls still if you don't stand out somehow.
The whole "just shave it" is said by either dudes who never experienced hair loss or if they do, won't happen for many years or have other things to make up for it.
The reason that we go all out to be test rats and spend thousands on research projects, use treatments that would be considered outdated in today's incredibly speed-increasing science/medicine advancements, and cry and lose our minds psychologically is because while other science and medicines are reaching futuristic science fiction levels of research and technology, we're still stuck in the late 90s-early 2000s with what we have for hair loss treatments.