No matter how rough the means, those without strength cannot play the game. Not to mention the initial capital investment, just figuring out how to hook up with the Russian Aristocracy is a challenge.
As you know, the Russian Aristocracy is one of the most conservative entities in Europe. If a capitalist wants to make a sales pitch, they probably won't even see the person before being driven out.
Even if the sales pitch is successful, if they encounter a greedy noble, there's also a chance that someone will just default on the bonds, and in the end, not a penny can be recovered.
Though Franz wasn't worried about competitors, he still kept his work secret. Otherwise, if the Tsarist Government patched things up beforehand, all he could do was wait for Alexander III to repay the money.
On the surface, this era seems like the time of the gold and silver standard, where currency seemingly did not devalue.