My guess-lack of funds in 90s and huge stocks of RPG-7; purchases of PG-7VR grenades was more cost effective solution(since PG-7VR have same armor-defeating capabilities as PG-29, albeit at shorter range). ...And, in order to reliably kill modern MBT you need something with penetration exceeding 900mm; to achieve this warhead diameter should be about 125mm. In other words, RPG-29 is obsolete for a long time.