I registered a few years ago as a US military customer required it for purchasing (others didn’t both before and after though even though this one customer insisted that it was impossible for them to purchase unless registered, go figure). Lots of pages and most q’s not relevant but not too onerous as I remember.
re: “Surprised that you are not on” - unless you target a local/federal govt niche then I am surprised that they would surprised! There are lots of these sorts of registration sites, federal, state, local and much of the premise behind them is not relevant to software (its for commodity services work or commodity supplies so “pick up a $ share of Govt contracts!” == “you get a RFP for each and every IT project from $20 to $2bn regardless of fit”) so IMHO its just not practical, feasible or even worthwhile registering unless you’re in the niche of B-2-Govt.