I think they have not developed or coded their platforms according to the required model of erc 20 tokens, furthermore they do not provide the private keys to the user that make them partially owned wallets not fully owned one.
Hey, thank you very much for your response! So at the moment there is now provider allowing the integration of ERC20 wallets? I've read that coinbase could be planning to implement these in 2018
https://www.reddit.com/r/0xProject/comments/7dnr8s/coinbase_likely_adding_erc20_tokens_in_early_2018/ but it would be interesting to know whether there is already a provider supporting ERC20