My house is wired with 12/2 Romex and 20 amp circuit breakers. However, I happened to notice that the switches that were used have a 15amp label. I was surprised to find that, I thought it would indicate 20amp. I checked other switches and they were all the same. Is it normal for electricians to use 15amp switches with 12/2 (20amp) circuits? I went to Home Depot and found that all the switches for sale were 15amp. Do they make or sell 20amp switches? I couldn’t find any.

There are 20amp switches, Leviton makes them. However unless you are switching heavy loads, they are not necessary. Note that you most likely have 15 amp outlets too, but they are allowed on a 20 amp. Circuit. If your outlets don't have a
"tee" shaped inlet on the receptical, you have a 15 amp outlet.
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I agree with ma0641,
The electrical code generally allows a 15 ampere rated switch to be used as long as the load is connected to does not exceed some percentage of it's rating. The code section is 404.14.
For most (almost all) things that one would be connecting to in a residential application, a 15 ampere rated switch can be used with loads not exceeding the ampere rating of the switch.
Now there are some types of applications where the load is limited to 50% of the ampere rating of the switch (Inductive loads) and motor loads where the load is limited to 80%.
This was a good question...