Firstly there is a distinction between functional hobby greenhouses and those intended to be ornate. If the greenhouse is built with creative architecture in mind the goal is aesthetic. We'll be focusing on functional greenhouses in this answer. The purpose of any sort of functional greenhouse is to create the best growing environment possible for your crop.
Commercial Greenhouses Are:
Designed to create profits and prioritize efficiency
Often more exposed and require thicker steel, more bows (smaller sidewall spacing), and other more robust materials
Scaled to produce cost-efficient harvests, with footprints ranging from one thousand to one million square feet
Structured with practical features like larger doors at each end
Designed to accommodate more elaborate ventilation systems with exhaust fans, intake shutters, and light traps
Built to accommodate all phases of production and adequate room for employees to work comfortably
Integrated with environmental controllers and all necessary equipment to optimize growing conditions
Hobby Greenhouses Are:
Designed for fun as much as production
Usually less exposed to the elements wedged between residential homes
Sized smaller to require less labor intensiveness
Structured in a less robust way which saves on costs
Usually include simpler ventilation like roll-up sides
Sometimes comically sophisticated as a result of an owner/operator going hard on automation
Hosts to a variety of strains and sometimes entirely different crops which can change how "purpose-built" they are