I don't think they need to test new strategies as long as the ones they're using are still good and profitable. I wouldn't force myself to use a different strategy if I was already profitable with the same one - but it might require some adjustments over time. The change of strategy is necessary if the previous strategy is no longer profitable - maintaining it will only be detrimental.
After all, in trading one does not need to chase the maximum profit, it is enough to take profits consistently at a predetermined percentage. This kind of trading approach will not put traders under pressure due to uncertain price volatility.
I think that changing a strategy is a very difficult step. Look, when you first started trading, you spent a lot of time testing different strategies to find one that works for you. Maybe you modified it, added something of your own, and it started to work and bring you profit. And to replace it with something else, you would have to go through the same process again.
But in my opinion, if you haven't changed as a trader, if your view of the market hasn't changed, then you'll still end up with the same result, the same strategy. That's why I think it's very difficult. Also, a strategy can perform differently in different markets, and that could also be the reason.