Firstly, from the BC Ferries website:

Accessibility options available on board larger ferries travelling between Vancouver and Vancouver Island:

• Accessible passenger areas and cafeteria
• Designated priority seating
• Elevator access (see more below)
• Induction loop hearing systems (see more below)
• Ramps to board the ferry

That implies smaller ferries by BC Ferries don't have the same level of accessibility.

Second, BC Ferries is the operator on behalf of the BC government, so I think there is more of a push for better resident access, which BC Ferries holds Accessibility Committee meetings for. Hullo on the other hand is a private ferry company and so their priorities and the purpose of their vessels might be different, accessibility not being at top of mind over capacity, speed and availability of service (which translates to profit). Different regulations apply for vessels built for different purposes (the BC Ferries are not made for higher-speed journeys for example).