I can't say I've seen him, but one hurdle might be the entry level system. Kovar would be free (assuming his KHL contract is up) to sign a contract without restriction next offseason. But up to this point, he would have had to sign an ELC (925K max guaranteed plus potential performance bonuses).
Kovar might have stood to earn more money by staying in Europe until he was old enough (27+) to get around entry level provisions. Roman Cervenka signed his CBA mandated one year ELC when he signed at age 26. Cervenka had some success but possibly left some money on the table by not waiting a year.