You need a low/moderate impact web app, you only need bread and butter infrastructure, django/ruby/node app, postgres, redis, basic autoscaling. You (your agency) does not have experience doing this (for example, you’ve never built something on remote-hosted infrastructure before, you’ve never built anything that wasn’t locked to windows before, you’ve never done anything that wasnt hardcore waterfall before, etc). You wouldn’t know where to start if someone asked you to build a web app that would be easy to find technical talent to support going forward (you just assume this means a building into a Microsoft product). You don’t know why open source software makes your life easier when maintaining a software system. More charitably, you want try this “agile development” thing that everyone is talking about, and you need air cover to keep your IT dept from demanding that you give a contractor 500k-1.5m to put up a “secure” boilerplate, ‘hello world’ modern web app deployment that will kick off your agile dev process, which ought to take one person a week to deploy and another person a week to lock down.
There are a surprising number of agencies and departments that meet the above description, but either they don’t know what cloud.gov is, or equally likely, their IT department would rather spend a lot more money on a contractor and feel like they have more control. There is zero incentive to take a chance, even if you can be reasonably sure you’ll get as good or better infrastructure for 1/5 or 1/10th the cost. No one will be impressed that you saved the money and you’ll live in fear for years that something will go wrong and you won’t get promoted because you chose a scary new thing and it backfired.
They’re (IT) also likely to understand a “web app” as something tightly coupled to their existing systems (meaning they cannot imagine their existing systems securely communicating with an external, independent API, even they themselves built it) which pretty much excludes all modern software practice and excludes using cloud.gov to build additional capability.
If a potential client already knows how to build, deploy, secure and get their IT dept to authorize an aws-hosted modern web server, they’re not (at least right now) a target audience for cloud.gov, but I don’t think that describes most agencies or departments