The reason why suppliers avoid e-invoicing is because they do not get the advantages. Do you recognize this pattern:

• A buyer invites you to a bespoke e-invoicing solution
• The solution relies on specific document syntax and content requirements
• As it is a buyer specific, the expected lifecycle is uncertain and re-use limited
• The more solutions you support, the more resources you need to maintain

In summary: there are no economics of scale to be found