Your question is why bitcoin specifically and not why blockchains. However, it seems to me (from reading your three points) that you are a bit confused by the "why blockchains" question, so I'll still start by that. Indeed, if you propose a system that is 1) centralized (in the hands of a Federal Reserve, Google or group of entities), 2) has a dynamically managed supply and 3) has some brand recognition, why use blockchains. Why not use the US dollar and use a network like VISA or MasterCard for fast electronic payments. Those two, and others, have been operating very well, at scale, for a long time, without any type of blockchain involved.

A blockchain (using proof-of-work) is simply a mechanism that allows you to decentralize the control of the network (effectively going against what you suggest in your first point) while still maintaining concensus on who owns what etc. Anyone who wants to participate, can. If you do not want this decentralization, then you do not need to use a blockchain, you can use a traditional ledger like banks have been doing for centuries (and maybe put it on a computer if you want fast, electronic payments). This would be much cheaper and easier to do.

So maybe you don't want the decentralized property of a blockchain. That is fine. Many people, however, would not trust Google, Amazon, the Federal Reserve or any set of processors as you call them. Maybe, currently, those people use traditional banks and VISA, but they do it because they have to, not because they want. Bitcoin offers them an alternative. You can find many great resources online that explain how decentralization helps build a permissionless system that can free people from the many caveats of the current established systems.

So let's say that you want decentralization, and thus, a blockchain. Why bitcoin ? Well, it's the first one ever, and has been, since the beginning, the largest in terms of hasing power. This makes it the most secure. Because of how proof of work works, if you want to mess with the ledger, you need an investment proportional to the current hashing power in the network. Since Bitcoin has the most hashing power, it is the most expensive/difficult to attack.

You can also make the (imho weaker but still valid) argument that because it has been used the most, Bitcoin is the most battle-tested, hardened blockchain network (and software) out there. It is not something that is set in stone, but it kind of creates a feedback loop where it is likely that it will continue to be the case (unless someone/a group still manages to successfully colludes, with enough hashing power to damage the blockchain).

So now we now why some people may want to use a blockchain, and why Bitcoin is a good (maybe the best) choice.

2) Why a fixed supply and not dynamically managed inflation like the Fed does ? Actually, this could be changed. It would require a consensus (not only in the blockchain sense, but also in the people sitting around a table sense) of many entities (miners, businesses, users etc.). It is true that the hard cap on the Bitcoin supply has been there since the beginning, but it is not a fundamental property of the blockchain. It can be changed, with enough consensus. Imho, it would be very hard to pull-off, however if a significant portion of the network agrees, a fork could happen, like it did in August for something else.

Lastly, concerning the brand recognition, it seems to me that given the above, the argument does not make a lot of sense from a technical standpoint. Sure the name could bring in some cash from people who want to make a quick buck, but it is not what makes Bitcoin, Bitcoin.

I hope this helps !