You have to be careful with terms in this space (and many of them aren't even well defined).
There are algorithmic trading strategies that are high frequency, but not low latency for instance. Or low latency strategies that are not high frequency.
In my experience what people are talking about when they say that high frequency algorithms are producing less profits, what they really mean is that low latency arbitrage algorithms are not making as much profit.
Lots of high frequency algorithms remain profitable.
There are algorithmic trading strategies that are high frequency, but not low latency for instance. Or low latency strategies that are not high frequency.
In my experience what people are talking about when they say that high frequency algorithms are producing less profits, what they really mean is that low latency arbitrage algorithms are not making as much profit.
Lots of high frequency algorithms remain profitable.