Enamel does not chip because it is badly made. It chips because it is glass, and glass behaves in predictable ways.

The rim takes almost all of it

The lip is knocked against taps, stacked against other mugs and dropped rim-first. If there is glass at that point, it will eventually lose.

A rolled rim removes the glass rather than trying to toughen it. The steel is folded over on itself and left bare, so the impact point is stainless. It is not a premium feature and it should be standard on anything sold for daily use.

The other cause is the steel, not the glaze

Coatings cannot bend. When thin-gauge steel dents, the enamel over the dent has nowhere to go, so it crazes into fine cracks and then lifts away in a flake.

This is why identical glazes behave differently on different mugs, and why a heavier gauge is the real durability upgrade in a commercial room. The chip you see is the last step in a process that started with a dent.

What a chip actually means

Under the enamel is mild steel, so an exposed chip will develop a rust spot. It is not dangerous and it is not going to spread under the surrounding glaze, but it will look worse over time and it is where most mugs get retired from front-of-house.

Dry chipped mugs properly rather than leaving them wet in a rack, and they last considerably longer in that state.

What does not help

A thicker single coat. Coat count and coat thickness are not the same thing, and a single heavy layer is more prone to crazing than a ground coat plus covers.

Buying a heavier mug for a shelf. If it is not being dropped, gauge is money spent on freight.

Anything described as a protective coating over the enamel. Enamel is glass; there is nothing to protect it with that is harder than it is.