I'm using debit card since the early 00's and I've owned a couple of credit cards in the past 10 years. What I find the most inconvenient in using both cards are the limitations and the fees.

 Limitations: you cannot withdraw more than 400 lv per day from a debit card in cash (this can be changed but I don't think it's very easy to do); your money is not insured against theft if you use debit card, and I have a lot of friends who's money has been stolen from their debit cards using scanning devices on ATMs; 

Fees: Each ATM takes a different fee depending on the operation you make and the bank which issued your card. Fees vary from free (if the ATM is owned by the bank that issued your card) or 0.55lv per transaction to 3% of the amount you withdraw (or 12lv! for every 400 you take from the ATM). And this is just for debit cards. 

Credit cards are a whole different stroy - banks take even more money in fees, and the interest on debit cards is often as high as 19%... It proves to be very expensive for the Bulgarians to own and use a credit card - so I think the banks are working against the wider use of cards in BG.