There is a 1.11% chance of getting cosmetic item from a commendation chance according to these stats (proof). Which means there is a 98,89% chance of not getting a cosmetic item in a commendation chest. The chance of not getting a single cosmetic item in 800 chests equals to 0.9889^260 (raising 0.9889 to the power of 260). The result is 0.0549, which equals to about 5%. That means that 5% of players will not get any cosmetic items even after opening 260 chests.

And even after opening 400 chests 1% of the players, which is about 160 people, will still not get any cosmetic items. Fun fact, this calculation is confirmed by the data itself, where at one instance there was no cosmetic items for 370 chests in a row.

Now live with it.

P.S. On average you get 1 hat per 90 chests.