Sounds like an online [bucket shop](
https://en.wikipedia.org/wiki/Bucket_shop_(stock_market) ). And seems like it's a much worse proposition than the actual stock-market.
With real stocks, shareholders buy/sell in a manner that might be compared to gambling for some. And if those were the only cash-flows, then the stock-market would be a zero-sum game. But they're not; the stocks entitle holders to other cash-flows, e.g. dividends or asset-distribution to shareholders -- so the stock-market isn't zero-sum.
By contrast, such gambling platforms would seem to have cash-inflows only from other gamblers. And additional cash-outflows to cover incentives to miners, etc., to keep the block-chain operating. So while the real stock-market might be better-than-zero-sum, seems like these would be worse-than-zero-sum.
So.. why? I mean, even if someone just wants to gamble, why not gamble in a net-positive system rather than a net-negative system?
(Also this sounds like it might be illegal in the US and perhaps elsewhere.)
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To sketch a simple example:
Alice starts a company with $1,000 of her own money, creating 100 shares (valued at about $10/share). She sells some of her shares to others for ~$10/share.. let's say she sells half, so she gets back $500 while retaining a 50% stake in the $1,000 pot.
As CEO, Alice invests all $1,000 in US bonds, getting some interest. After 10 years of operation, Alice liquidates the company, which now has $1,000+(10 years of interest).
Now everyone who bought a share from Alice at the start (for ~$10) would get about ~$10+(10 years of interest), much like if they had invested $10 in bonds themself.
And Alice herself gets back $500+interest (in addition to the $500 she got from selling shares earlier).
Now what about people who gambled on Alice's company? This is, now that Alice's company has dissolved and the real shareholders got their cash+interest, what do the people with "synthetic shares" get?