Have you ever done it? Cause it's not as trivial as you make it sound
Indeed, the guys who did pure latency arb have consolidated a lot, but that process feels done to me. Lack of volatility a few years prior to 2018 has made it worse for sure. These days, howver, I don't see as many CVs from Jump or Hudson River as I did I in 2017, which makes me think that they are making money again. Top tier latency (let's say sub 5us tick to trade on a futures exchange, though there are much faster guys out there) is very expensive and infrastructure intensive, so it's natural that only a few survived this arms race.
Second tier latency (say 10-50 us t2t) is more accessible and almost can be bought at retail level. The only problem is that at that level of latency, speed will not make you money. So guys who are doing something slower but smarter (e.g. Tower Research type setups) are doing reasonably well. People who are providing across multiple time frames (like my team, as I am both turning the book a fair bit intraday as well as holding a lot of overnight risk) are doing all right. I guess in your definition it's not really HFT, as it actually requires taking some modicum of risk and understanding of the market.