>> This decision is unethical to full-time employees
It's easy to mark any decision as "unethical" depending on your viewpoint. Indeed ethics are, to a large degree, highly subjective.
I might suggest that eating meat is unethical, or I might think whaling is unethical but beef farming is ok, or I might be completely ok consuming any meat since we're omnivores and meat is part of our diet. None of this is material though, and all points are equally valid, since ethics are subjective and personal.
So I've no problem with you considering this unethical, or even mentioning that you consider this to be unethical. An employee, who didn't negotiate an appropriate contract, would likely feel bad about this, and would thus maybe fall back on "unethical".
However from a business point of view it's completely ethical. The contract between an employer and employee is a simple business relationship. Their responsibilities and powers are clearly laid out. Setting increases and bonus's is clearly (for most of us) a mandate given to employers. In some cases (where unions are involved) the mandate falls over both the employer and the union.
Of course employers care about employees (in most companies anyway.) If only because a mass departure would be bad. They also have other considerations though, customers, shareholders, sustainability, future profitability and so on. They are constantly balancing many levers to try and keep "everyone happy". Usually this means the love has to be spread around a bit, not everyone is going to get everything they want.
Does this mean it's always in balance? no of course not. Currently (in the US) there's probably too much of a lean towards shareholders - both in artificially increasing stock prices, and also in prioritizing returns. In other places labor is stronger and the balance is away from shareholders. In another time, and another place, there's reasonable balance for a while.
For me personally, it's hard to feel sorry for FAANG employees, who've been living large for years and now (shock, horror) aren't going to get increases. Oh no, that 100K you're getting isn't enough? My heart bleeds for you. Said no Uber-driver ever...