Just to elaborate a bit more, 1x1 convolution is often used to reduce the number of parameters from the previous layer to keep the total number of parameters manageable.

yes, thank you, I understand the motivation, the reason I never understood before was quite simple, the description "1x1 convolution" (correctly) described that they were not doing convolutions across pixels.

It is good to point out what they aren't doing, they should also point out what they are doing.

Humor me by considering:

"Today I did not go to the zoo, I did not go to school, ..., and I did not go by foot, nor by vehicle without weels, nor by a vehicle with only one wheel, nor by a vehicle that had 3 or more wheels, and the vehicle was not motorised, and I did not need to stand up on the vehicle"

While true, and possibly important to point out what I didn't do, it's generally more helpful to describe what I am doing, like "I rode my bicycle to the supermarket"