VCs have a whole staff of people needed to do business and a ton of costs. There's a legal team, marketing/events, human resources, finance, some executive assistants. Screening, meeting founders, traveling to meet founders, takes up a TON of time and obviously most of the time, no investments are made! Also don't forget, VCs have an office, usually not in a cheap place, so lease costs, cleaning costs etc.
If VCs had to work for free, where would you be meeting them? Ok it's all virtual now, let's say. But the truth is, meeting people face to face when you're going to write them a cheque for 10-20M is generally a good idea. So VCs and founders will almost always need to travel. You're also always going to need lawyers and finance people, since you're dealing with term sheets and large amounts of money.
As others have said, VC investments are not liquid at all and the timeline is 10 years for any returns. So a VC investor in your world has to travel around the US, Europe or India meeting founders, has to work with lawyers, financial folks for free, gets zero benefits in terms of healthcare, etc. All for the chance at 40% of something in 10+ years, that might not work out anyway?
If run this way, the industry would simply not exist and the founders would not get any investment. And the truth is this, there are many founders out there who want and actively seek VC investment and "shock" actually are happy with the relationship with their investors because they understand a good relationship benefits both parties in the deal.
I will also add, most employees in VC firms get no percentage of the profits of the fund (i.e. the carry). Most VC employees just get a regular salary (which is often far less than tech company salaries). So if there were no fee associated, these people would never get paid, since even when the fund finishes, they wouldn't get any of the 20% carry.