1. It's expensive and time consuming to get to.
2. The infrastructure at Bulgarian resorts does not compare to what a North American skier will find at a major destination resort in the Alps.
3. Snow conditions are not as good as the Alps.
I've never skied Bulgaria but have done summer surveys of resorts in Slovakia, the Czech Republic, and Poland. I also lurk on Slovak language ski forums. When you have Slovaks telling other Slovaks to spend the extra money and go to Austria, something must be wrong. As we all know, you can get twice as much skiing accomplished at a resort with high-speed detachables and high-speed gondolas than one with old POMAS and slow chairs.
Bulgaria might be a good choice for an adventuresome Swede or Brit who can catch a cheap domestic flight to Bulgaria for a long weekend, but for Americans and Canadians, I don't think it is a good idea unless you are more interested in experiencing a unique culture than skiing.
One of the big costs of skiing in Europe for North Americans is the air ticket and car rental costs. Everyhing else is not terribly expensive by our standards. That's why I always tell poeple who are first time visitors to European resorts to go to a flagship, snowsure resort first:
Courchevel 1850 (intermediate skiers)
The Arlberg (Lech for intermediates/St. Anton for advanced skiers)
St. Moritz (intermediate skiers)
Val D'Isere (advanced skiers)
You can always save some bucks by booking at a two star, but if you are traveling to Europe primarily to ski, don't pick a 2d tier resort. Go for the first tier--a snowsure place with new lifts where you can easily bag 40K of vertical a day.
Don't get me wrong. I love Eastern Europe and have travelled extensively to Slovakia, Czech Republic, Poland, Hungary, and Romania but these places are better bets for hiking and mountain biking than skiing right now. Things will change quickly, but for now, ski elsewhere.
Bulgaria doesn't use euros - dunno if they are accepted there however.