why do I have to answer sustainability questions as a supplier

Your customer is preparing his own CSRD reporting

Your customer is asking you this because he is himself subject to reporting obligations under Directive (EU) 2022/2464, better known as the CSRD. That directive requires large and listed companies to report on their entire value chain, including suppliers. Your customer can only complete this if he collects from his suppliers what he does not know himself: energy consumption, emissions, working conditions. That is called scope 3 when it comes to emissions, but the questionnaires you receive often go broader, extending to governance structure and policy.

The format varies greatly by customer, and that is precisely why the same answer comes up dozens of times. Some customers use their own list, others align with the EFRAG VSME, the voluntary standard that was specifically created for SME suppliers that are not themselves subject to the CSRD but are being asked by customers that are. That standard is a good indication of what you can structurally expect: basic company data, environmental indicators, and a few questions about governance. Evidence is usually an energy bill, a policy document or a CO2 calculation; if you do not have those, then "no" or "not applicable" is a valid answer, not an obstacle.

Traceable to the value chain requirement of the CSRD

That suppliers receive this type of questions does not follow from a direct obligation for the SME sector itself, but from the value chain mechanism of Directive (EU) 2022/2464: reporting entities must include material information about their value chain, and that information comes from suppliers. The EFRAG VSME module is the direct response of the standardisation world to that pressure: one fixed format, so that not every customer keeps inventing his own list. Basic data such as the sector in which the enterprise operates and the number of employees appear in almost every format, because they form the context in which the rest of the answers are read.