Why are Android boot times relatively slow?

Original question by @monovergent@lemmy.ml

The storage and processing power of modern smartphones are touted to rival those of a typical laptop. Yet, my trash-picked testing system from over a decade ago with a bottom-of-the-barrel SATA SSD can still boot to the Linux desktop faster than all but one of my Android devices.

Understandably, this isn't a huge priority since very few people are cold booting their phones every morning. But is it just plain unoptimized? How hard would it be to optimize? Do security features and checks bog it down? Is it that there's many tiny files to load when booting? What gives?