Ingredients need to be online as well as on the product for a couple of reasons.
Transparency – it’s not enough to say “oh look at this active ingredient you’ve been asking for” I want to also know that the product doesn’t contain harmful ingredients
The micro-print that some companies use can be impossible to read even with a magnifying glass.
It’s easier to search a website page for your allergy than to try and sort through dense text (worse when it’s both dense and tiny.)