Since most of the major altcoins move up or down at the same time as bitcoin, aren't they all controlled? How does it work?

While it's true that Bitcoin tends to have a significant impact on the overall cryptocurrency market, it's important to note that this correlation is not absolute. Altcoins can and do move independently from Bitcoin, and their performance can be affected by a range of factors such as project updates, adoption rates, and market sentiment.
It's also worth considering that the cryptocurrency market is still relatively young and volatile, which means that even small changes in demand or market sentiment can have a significant impact on prices. This can lead to a situation where the movements of different cryptocurrencies appear to be more closely linked than they actually are.
At times, the value of Bitcoin has experienced a decline attributed to the inadequacy of certain alternative cryptocurrencies, as seen in the FTX case. Market behavior is often influenced by current events and patterns, and strict regulatory measures can occasionally result in market downturns. Conversely, there have been instances where Bitcoin has experienced a downward trajectory while alternative cryptocurrencies have seen an increase in value.