I think the explanation is simpler: they're simply incompetent. They grew too fast. They went from about 20,000 users online in Feb to over 40,000 users a month later, and they simply didn't plan for that kind of growth. Everything is falling over on Polo, the wallets arn't being maintained, new users arn't being verified, large withdrawals arn't being authorised in a timely manner, the platform keeps crashing.
My advice: use either bittrex or HitBtc for steem trades. The only reason people are dependent on Polo is because that is where the volume is. But we can build it up on other exchanges.