Simple question back to you: Why are there investment banks, mutual trusts, hedge funds etc. that are offering their services to the public???
Investment companies are not offering investments that (historically) claim to generate about 1% per day. If they have ways of generating those kind of returns, they won't be sharing them with you and me.
Because making a large profit off of arbitrage requires both liquidity (provided by the exchanges) and a large amount of capital (provided by either the business or investors), and they may not have that much to invest on their own. With other people investing, they make significantly more profit. If you have 1$ to buy gold on one exchange, to resell for 2$ on another exchange, that's great. But you still only make a dollar. Now, if you had 1 dollar and 99 other people to invest 1$, suddenly you've made 200$ off the trade, and you share out the profit to the investors, plus a cut for yourself because you took the time to find the arbitrage opportunity and perform the trades for the investors.
I am not convinced one way or the other, but from a pure business perspective what they're doing does seem viable. If I had the capital myself I could easily make 1% on arbitrage every day, but it requires you to keep both USD and BTC in large amounts on several exchanges so you can react to new opportunities without waiting for cash to transfer everywhere.
Yes, I understand that you need a minimum amount of capital to effectively perform arbitrage. Of course on the other hand, there is a point where you have too much capital available.
I suppose eventually we will find out the truth, at some point they will wind down and we will see if they can pay or not.