Cross class skills: why does CNJ have botany and mining skills available?

[Anova]

The base classes are a relic of the 1.0 system, and allow players to access all cross-class skills from all classes. As you can guess, some are more useful than others, while others are completely useless for the class. The gatherer skills are simply useless on the combat classes but the game code was likely written in such a way that removing them causes instabilities or bugs.

The team is outright eliminating classes for future jobs in 3.0 heavensward, but I don't know if they'll rewrite the current game code and remove classes altogether. It's a lot of work to fix something that has relatively little impact on players. Most just ignore them although there is a small minority of players who want all the cross-class abilities accessible even if they will never be able to play publicly with those subpar loadouts.

[ruskie]

The team is outright eliminating classes for future jobs in 3.0 heavensward

We only know that DRK will be a base job. We have no info if they are getting rid of classes outright. There might be lore reasons for this or they might actually be working towards this. I doubt though that they will ever remove the base classes that are in play now.

[Niwashi]

The base classes are a relic of the 1.0 system, and allow players to access all cross-class skills from all classes.

Not quite all. The crafting cross-class skills, for instance, are only crossable to other DoH classes, as there would be literally no way for a class that doesn't craft to use them.

And while some DoL skills (the ones pertaining to finding gathering nodes) are crossable to DoW/DoM classes, the level 20 ones (Byregot's / Nald'thal's / Thalik's / Nophica's / Menphina's / Llymlaen's Ward) are cross-class-able only to other DoL classes, because those ones can only be used while gathering. (I believe in that case, the actual rule is that they're assignable by any DoL class, but really it's only useful to cross the BTN ones to MIN and the MIN ones to BTN. FSH has no use for any of them, but I believe is still allowed to assign them to cross-class slots anyway.)