There are several reasons:
Stores that offer these games have no operating contract with publishers, allowing them to have no minimum cap on the price.
Most games do not have physical boxes so they do not require transport neither packaging therefore this reduce the price even more.
Games sold digitally are not subject to the same VAT system as physical ones therefore are much cheaper.
Stores that sell these games have lower operating costs than for example Steam or Origin, that allows them to reduce their margins to make product prices much more attractive.
*If you need assistance or have any other questions you can contact us through our live chat support (bottom right) or email us email@example.com, we will be more than happy to help you.