I agree with Wally.
I also see no point in challenging the accepted standard. Many reasons have been posted here as to why this TRAINING EXERCISE could or could not be conducted at a lower altitude....for eg a DC3 needs more room...
Keep it into context..the original Q was posed for ab-initio.
I'm glider initial trained. I like many others from that genre did my spin training, not above 12-1300 agl. Theoretically I am comfortable with it.
Consider power instructors, their spin experience, is most likely limited to what they did during their rating.....99% of GFPT/PPL holders have never done a fully developed spin. Glider pilots spin every type they fly, and practice until the reaction is automatic, even in a look away situation.
I'm comfortable in spinning and stalling, but given the choice, i'll have the 3k AGL option thanks.
Student learning + Instructor that might not be comfortable...all the room we can get regardless of the dollars