[Maciek416]

I think conserving energy in cold months is close to the biggest factor.

Regarding the dropping of biomass, in both deciduous and evergreen species, some of the substances from the retiring leaves/needles are reclaimed by trees ("retranslocation") and pulled out of the leaf before letting go of the leaf. In species like pines it'll be the second or third (or older, sometimes much older) retiring needles and in species like maple or beech it'll the be the entire foliage. Mass useful to soil ecosystems still falls but the tree grabs what it can in the late months of the year, hence the color change.

One thing the grandparent comment doesn't talk about much is the cost (in sugar) of both building and thereafter maintaining leaves and the related tradeoffs. Building a fully winter-tolerant broadleaf is more expensive sugar-wise than building a winter-interolerant leaf. A sugar maple in Quebec, where the season is shorter than (say) Oregon is going to compete in its niche better if it can attain surface area quickly at the start of the growing season, and that is better done with a winter-intolerant, more relatively delicate leaf. An evergreen leaf takes more time and mass to build and has to have more limited surface area or armor (cuticle) to tolerate such winters.