You can develop a days worth of vitamin D in 15 minutes (or simply supplement it for the same benefits), meanwhile excessive sun exposure is correlated with all manner of health problems, not the least of which is cancer. People who spend more time outdoors tend to die younger.
People who spend all their time indoors (in front of screens) will seek to justify their lifestyles, just as those who spend their time outdoors will seek to justify theirs. There is nothing rational about pre-supposing that your personal habits represent some sort of optimium: it is only through careful study that benefits and costs may be determined.
Again, progress trumps tradition.