Tuesday, 8th March 2016, 18:53 by Jarlyk
A few reasons that come to mind for me:
1. Really early on, spell hunger feels 'scary' (or at the very least, annoying), so you prioritize getting rid of it. Eventually you learn to pretty much ignore hunger as a mechanic, as much as the game lets you.
2. When you're new, you don't really understand noise (honestly, I still don't fully understand it) and conjurations tend to be noisy, so you're likely to end up fighting extended battles. This means that you burn through more MP, as you have to fight longer before you can rest. Eventually this becomes less of a problem, as you start luring more (keeping the encounters smaller) and, if using particularly noisy spells, you might retreat from where you fought most recently before resting/channeling. I often still train Spellcasting more than is optimal for the MP, just because luring annoys me. If you make good use of luring and various forms of dancing, you don't really need the extra MP, since you either keep the encounter small or you employ a degenerate tactic to regenerate it safely during combat.
3. The skill you should probably be training instead (Fighting) doesn't sound like something a 'mage' would use. Mages have a long history of being the glass-cannon archetype in RPGs. The trouble is that glass-cannon and perma-death don't go together especially well, particularly in dcss, where games can run a bit long. Defensive skills offer a buffer against mistakes and, if the game runs long enough, a few mistakes are pretty much inevitable. Crawl combat has enough variance that particularly fragile characters can be one-shot in some encounters, which is a huge risk to be walking around with.