Perhaps SP Tech doesn't have the funds to refund customers now. Also, the venture capitalist/private funding people will get paid first most likely, these people make perhaps 500% on their investment so I would also guess that SP Tech paid these people from the Pre-Sale Funds.
Hope I am wrong
Typically, angel investors get paid after a certain amount of time according to a % of EBIT or revenue.
This period is almost never below 4 years.
Additionally, Angel investors typically profit from an exit scenario according to a percentage of their original funding.
Bitcoin Mining Hardware Design Business is not Typical and I am sure you know that, 4 Years is very long time in this business, I am pretty confident that investors are getting paid but we will never know due NDA.