Part of the problem with building facilities is that you're tying up resources that could be allocated elsewhere. When you start building, the funds are deducted from your account immediately, but the building takes time to construct.
If you can't finish a satellite facility before the end of the month, you've taken a chunk of change out of your account that has no benefit for the current month. You can't launch new satellites and get your money's worth out of your investment before the new month rolls around. At that point, you'll have more cash available.
Therefore, it's possible that you could get some sort of benefit out of these resources by allocating them differently in the short term. Maybe a bit of research will complete, and you can devote those resources to building something that finishes immediately, or perhaps you'll get hit by something you're not expecting (loss of an interceptor, a council request, etc) and can use the cash to deal with the evolving situation.
Also note that one of your assertions is incorrect - you can build satellites without uplink capacity. There's a warning on the build screen for the satellites, but you can ignore it if you wish. Therefore, at the start of the month, you can start building both the uplink and the satellites, and launch them in the same month.