Having trained in desktop QuickBooks, I nearly panicked when called upon to work with QuickBooks online and at first didn’t even recognize what the hell I was looking at. Fortunately there was enough commonality that with a basic understanding of accounting I was able to figure it out. But still, why did Intuit do this?
A web application is necessarily different from an installed bit of desktop software, it actually takes great effort to try to make them similar.
I think quickbooks has used an off-the-shelf template and framework for their online version (I think I recognise it as the same one my web dev has ueed for a customer portal at my work). The template contains lots of lovely components such as graphs, charts and menus, but tgey come as a package - when developing content this way, you choose a theme and you get elements that have been tailored to fut it (or you have to invest effort in customising it, which sometimes breaks it, or looks horrible)