Why would any company want to directly list and be less secure? The only upside seems to be no lock up and direct access. Am I missing something?
Because slack is confident they can list and sell at the price they(slack and current investors) decide and the company believes in the stock hence they don't need underwriters(investment banks) to buy the stock at price decided by the banking firm.
Also, an IPO would bring additional dilution to their stock. Why dilute if you don’t need to?
Totally agree with that, but I was wondering more about the so called security
There are lots of reasons to sell a stock. If nothing else, you should expect that many employees have a substantial holding and want to diversify.