Yeah, it just isn't happening without a massive cooperative effort over generations. Not just the time for each generation of volunteers to be monitored, but also the work needed to address age-related entropy that isn't purely "lifespan" - no point splicing yourself into tortoise-person if you spend the next three hundred years as Joe Biden.

That's a selfless undertaking for tens of thousands who will never see the benefits and might suffer some real nasty side effects. Leaving aside whether or not it should be done in the first place, it's just not compatible with the Rich Man Afraid of Hypothetical Screaming Void impulse which drives modern life extension nowadays.