Two words: Pot holes
Metal on metal BJs hold up better to impacts. Yes they need greased every once in a while, but some people have the false believe that they need greased with every oil change, while it's more like every few years unless the boot leaks and if it does, you can't remedy that with the non-greasable joints unless you want to use a syringe and just hope that some grease makes it inside, but that can't flush out the debris that the torn boot allowed in. Possibly a new boot can be sourced, but by the time I'm taking the suspension apart enough to put a boot on, if the BJ can be swapped out, I'm swapping it out.
To me a non-greaseable BJ is like lifetime transmission fluid, lubed for life because the automotive manufacturer assumes no maintenance will be done, but the vehicle's lifespan (at least what the manufacturer cares about) is over before these parts fail - yet we're all about maintenance and hope our vehicles stay running past what the lifespan would be if never serviced (besides oil changes).