I find it very hard to understand why so many people and institutions are still participating in markets that are obviously full of insider trading. It's basically just giving money away to the insiders. Why do people do this?
Institutions do not stake their own money and are somewhat averse to the direction of the market. As for common people, they're generally not known to do the most rational thing.
You're a fund manager. What's the alternative? Throw your hands up and tell your customers to take all their money back, you don't want to get paid anymore?
There's no alternative
It's their job and if they're good at it, they still win / earn money. Someone who's staying eyes glued to the price charts on 12 stacked monitors will be the first to see a trend and buy/sell immediately after the action of the insider trader.