We know that Tzoirech Oichel Nefesh is permitted on Yom Tov. But this is only when it is Shaveh L'chol Adam (i.e. it is a need for everyone).
Some things that were shaveh l'chol adam in prior generations are not now, and vice versa. Two examples that come to mind are smoking and showering.
Smoking was permitted on Yom Tov because everyone who enjoyed smoking smoked. Nowadays this is not the case - many people who would enjoy smoking do not do so because it is known to be a health hazard. Therefore, this is not shaveh l'chol adam.
Showering or bathing was done infrequently, and therefore it was forbidden to wash one's entire body with hot water on Yom Tov. Nowadays, it is the rare person indeed who will go for 2 days without showering (and not only an istanis who will feel dirty). When there is a 3 day Yom Tov even more so - it is nearly unheard of today that an adult would go for 3 days without a shower. Seemingly, this is something that IS shaveh l'chol nefesh.
We all no that no Rav has issued a psak assuring smoking or permitting showering on Y"T. My question is why not?



