Launching on a risky booster, is risky.
You can define a risky booster as:
- First launch of a new booster.
- Return to flight after a failure.
- Booster with record of failure
So you feeling lucky punk? How much development money are you willing to risk on any of those cases?
Why did ISRO take the risk on the GSLV launch and Angara5 won't? I would assume that ISRO wanted to launch that payload, their boosters are not cheap, their budget is not unlimited, and they needed a payload anyway to demonstrate it. If they do not demonstrate confidence in their own booster, who will be confident enough to use it?
The Russians launch often enough on so many different classes of vehicles that they are not lacking options for payloads. They may not have had some project that needed a cheap-to-free launch giveaway. Also Angara-5 is a fairly large payload booster (49,000 lbs to LEO), so to really test it out you need a fairly big payload. Big payloads are usually high value payloads.
At that point it becomes a better choice to literally launch a ball of steel, or container of water. Something cheap, with good sensors to characterize the details of the environment inside the launch fairing so customers know what to expect.
Now if you had say a propellant depot in orbit, and you had a tug, then it would have made a ton of sense to launch propellant for the depot. Value is low if lost, but nice freebie if it worked. But we don't.
As for SLS, it is so expensive, and will be launching so infrequently it almost cannot be 'wasted' on a test flight. That to me is a design flaw. It seems like a full up series of test flights before humans fly on it would be part of man-rating. Atlas V will have had 60 or 70 flights by the time a human flies in a CST-100. Falcon 9 will likely be at 20-30 flights before a human flies in a Dragon V2. Why is SLS going to do it on the second flight?
It will be interesting to see what SpaceX launches on Falcon Heavy as its first payload.
I personally would love to see Elon Musk's original goal, a greenhouse on Mars, as the first payload (Huge overkill since that was planned to be tiny, and F-H has a huge payload ability). That is the sort of 'waste' of money they could do as a publicity stunt for vaguely cheap inhouse if the booster needed a payload no one else would pay for.