Could it be because the blockchain is overused?
Blockchain is not overused, not yet. Blockchain is spammed.
More casinos should accept other coins or create their own token coins to use on their own network so not to have these problems thus not having about 10% of those transactions contributing to the highest amount of unconfirmed on the slow blockchain as it stands.
I am fine with accepting other top altcoins like LTC, ETH maybe XMR that is all.
But I am strongly against creating new tokens by casinos, we should aim for unification not fracture ecosystem even more with more alts.
In the end you would be exchanging this gambling token for BTC in most cases anyway.