Did you have to deal with invoices from companies across 27+ different countries? Did you automate any of it at all?

Scale is a much bigger deal than the complexity of any one invoice. When you're dealing with hundreds of thousands if not millions of invoices from all over the place it makes sense to have it standardized so that software can be developed to do most your work with those invoices automatically and consistently.

I've worked on automating high volume document processing from a much smaller number of companies (mainly just from those within the US), just one or two outliers can massively expand your codebase and when those companies are free to change their formats on a whim in whatever why suits them it can break everything in ways that can be immediately catastrophic or very subtle but no less disastrous.