Why am i getting sick w typical respiratory infections (cold, flu, etc) more frequently & at greater severity (sniffles then vs bedridden now) than i ever had before, despite having a healthy lifestyle, no preexisting conditions, & good blood work?

It's just bad luck. If you are otherwise outwardly healthy, there is no like immune system problem that increases either infection risk or the severity of colds or influenza. Of course we're in the covid era, so that's a possible explanation. I hope you have been vaccinated (a few times) against covid and yearly against flu. Also pay attention to contact with people with similar symptoms.