I'm not sure what you're trading or what type of news you're talking about but I've never seen liquidity dry up on any of those KMEs I mentioned. Instead, I have on a few occasions seen liquidity lower but then suddenly pick up again in a reaction to one of those key market events (KMEs) and on other occasions the liquidity just stayed the same. Simply, overall the liquidity and volatility has increased...sometimes producing a trade opportunity. Other times there's no trade opportunity even though liquidity and volatility has increased.
I myself have only had little problems here and there with such such as when I'm in the middle of a trade and a KME sneaks up on me (I didn't know there was a pending KME). Anyways, I suspect you're viewing this differently than what others are viewing because there's different ways approach KMEs and news is just one type of a KME. Thus, you're right, on any given day there are many different types of other opportunities mainly because there's different types of KMEs.
Like I stated before, you gotta know your trading instrument because some key market events have no impact on your trading instrument while other types of key market events do have an impact. For example, unusual grain reports will impact grain futures while not having any kind'uv impact on Crude Oil CL futures. In contrast, many other types of markets are globally connected. Thus, certain types of market news out of China will increase volatility and liquidity in the Emini futures, Eurex futures and many other key markets.
Anyways, like I said, most using key market events are probably using it with chart analysis or DOM analysis...for day trading.