Here is an answer from 2016 by /u/NateOnTheNet (I don't know his/her Steemit handle) from the GRC subreddit which captures what you are asking about:
The goal of the Gridcoin project all along was to hopefully encourage people to contribute to BOINC in exchange for GRC. GRC doesn't necessarily need to be worth anything at all for this effect to happen, but obviously the more valuable it is, the greater the effect. So far, nobody is talking about directly financing BOINC projects with GRC that I'm aware of, but I don't know everyone who is participating in Gridcoin so who knows what's being dreamed up?
I think you're looking for an answer like "Oh, Gridcoin is going to do X and Y to make sure that merchants adopt it and millionaires buy tons of it to hoard" but there really is no such answer. A certain portion of GRC are being held in a foundation which is nominally intended to drive adoption by businesses and regular users, but there isn't any consensus yet on how those GRC should be spent, so for the moment adoption is being driven by individual users who think it's a cool project and want to get their hands on a few GRC either as an investment, to encourage other people to BOINC by making GRC more valuable, or for fun.
Over time, hopefully mainstream investors will become interested in building businesses around Gridcoin - it has some unique features that other cryptos don't - but right now you're going to be hard pressed to find any cryptos making headway with businesses other than Bitcoin just because it's the only one that has any significant public awareness outside of the crypto community.
Essentially, GRC is currently primarily rewarding users who were already contributing to science using BOINC for free. It covers their bills as the system stands. There is also opportunity for future BOINC projects to incentivise their project with GRC, among other things.
At the end of the day, Gridcoin is about turning the compute power from the crypto-scene into something useful to benefit humanity, rather than hashing aimlessly.