The difference is that unlike USSR bureaucracy, these corporations' continued operations depend completely on the decisions (buy or not) of customers who they cannot coerce -- so their feet are far more held to the fire of market reality than totalitarian regime leaders. They do not have the power to force people not to vote with their wallets (not to mention with their feet).
As frustrating and corrupt as our market economy is, the oppression under regimes like the USSR and East Germany was unimaginably worse.
That being said, yes -- we badly need another round of legislative reform like the Sherman Antitrust Act of 1890 and all the regulatory actions that followed.
In this day and age, that feels like something that is true in principle but not in reality. For food, the grocery store shelves are almost entirely stocked with brands owned by 10 companies, that have a combined revenue of $375 billion a year [1]. If you have a bad experience with DiGiorno pizza and boycott them, would you know you also needed to boycott Tombstone Pizza, California Pizza Kitchen, Cheerios, Tidy Cat, and on and on. If you wanted to actually boycott Nestle, how difficult would it be to maintain a spreadsheet of the literal thousands of brands they own [2]? Any issue with any brand is just absorbed by a thousand others. Any regional effort is absorbed by their global market. It isn't the USSR, but the idea that consumers can vote with their wallet just isn't the reality we live in anymore.
[1] https://www.the-independent.com/life-style/companies-control...
[2] https://en.wikipedia.org/wiki/List_of_Nestl%C3%A9_brands
> who they cannot coerce
If the market is a consumer need then yeah, these companies can coerce simply by being the only (or one of a few) options in town. Food, healthcare, and housing are all markets that appear to be narrowing which means increasing in their coercive abilities.
It's true that the USSR and East Germany were worse, but that had a lot more to do with the concentration of power into a strongman leader rather than the people. And, in fact, a major part of why West germany did so well wasn't really due to market forces, but rather due to the US spending ungodly amounts of money on rebuilding them (and Japan). The USSR was always pretty cash strapped. Especially since the only nations they could really interact with were nations under the USSR umbrella. Even other communist nations like China had pretty tense and often not friendly relations with the USSR.
In today's money, we dumped about $120B on West Germany. Just to put things in context.