I’ve built that before, many times.
It’s not a complication with Webflow, or with HTML- Webflow is just submitting whatever form you create.
Pipedrive just has a simple API with very atomic data structures, so it’s not easy to turn a lead into a full set of data structures that Pipedrive uses to represent it internally.
If you built this out yourself, very impressive 
most non-developers would have choked halfway through.