Fast video memory is expensive and in short supply. That's why you can't put much of it in ASICs. To make ASIC development unprofitable, most coins have a DAG file that grows over time. It means that miners won't buy a device that will be obsolete in a year, and it is too hard and expensive for the manufacturers to put double memory. So the coin ends up safe and only in the hands of video card miners.
Now Ravencoin needs almost 3.8 GB of free video memory, which means it can't be mined on 4 GB cards under Windows, but it can be mined under Linux, such as HiveOS and RaveOS. In summertime RVN will reach 4 GB, and it will be necessary to either switch to another coin, or to upgrade your video cards ;)
Check out our tutorial on how to set up HiveOS mining