and as I have no experience i am not even sure enduro’s are considered heavy.Maybe they are light for their purpose – esp compared to maybe the average full on DH bikes
I guess with XC type bikes if they are actually considered heavy then maybe it’s the additional material in larger wheels, forks that then have a larger gyroscopic effect to contend with, thus more strengthening or maybe at certain price points more material and maybe larger dimensioned , more highly strengthened frames, which again might add a bit of weight. However the overall result may actually possibly be a faster, more sure footed and enjoyable bike..with capacity to lighten if required.