The developers (at least important ones) could register with Debian project, just like they would with a company: submit identity and government documents, proof of physical address, bank account, credit card information, IdP account, .. It would operate like an organization.
The lead developers could meet and know each other through regular meetings. Kind of web of trust with in person verification. There are already online meetings in some projects.
2. Some people may want to remain pseudonymous for legitimate reasons.