https://www.financemagnates.com/cryptocurrency/regulation/sec-fines-etherdelta-founder-almost-400000/

Decentralized exchanges are still are subject to the law and may become more of a law enforcement target than centralized exchanges.

DEXs are now responsible for a higher percentage of money laundering of their total volume than centralized exchanges.

They are not really "decentralized" since the still has to be a team of people operating the exchange.

In the case of some DEXs they will still be vulnerable to hacks, 51% attacks and other coin network exploits.

It will be harder to hold the developers of decentralized exchanges liable since they may remain anonymous or live in a place other than where the prosecution occurs.

Waves Dex hacked. July 2018 https://cryptoslate.com/decentralized-exchange-waves-gets-hacked-after-6-million-debut/

Etherdelta hacked Dec 2017 https://mashable.com/2017/12/21/etherdelta-hacked/#LqdSbf4LJqqV

Bancor hacked July 2018 https://www.ccn.com/decentralized-crypto-exchange-bancor-hacked-12m-in-ether-stolen/

Newdex hacked September 2018 https://www.newsbtc.com/2018/09/18/newdex-decentralized-crypto-exchange-robbed-in-new-hacking-attack/