Your Amazon example proves my point. Even in the early days, Amazon had investor confidence because investors could see the value of their investment grow, because the machine Bezos was building reliably turned investment into revenue/customers. So they were willing to keep putting money in, even if Amazon in the early days lost money.
The opposite is the case with United.
We have invested Champs League money into a team that can barely deliver Europa League results, and we have done this consistently. We do not know how to invest money on players anymore. We are not able to generate the footballing return on our investment that our outlay demands, and that is why we are in the shit.
It is not penny pinching, it is not a "small club mentality". We are a listed business which could easily go bankrupt, like any business, if we don't manage our costs in line with our revenues.
What is the point of fantasising about financial solutions that nobody is offering? If we had a different owner, where money was no object, then that would be wonderful and we could do whatever we liked. But we don't. United has always funded its team from its footballing and commercial operations. We've just forgotten how.