I think the increasing popularity of DEX is due to these couple of reasons:
1.) Anonymity - Most Centralized exchange requires you to either do KYC for large withdrawals.
2.) Security - Just google 'crypto exchange hacked' and check out how many hacks happened in the past 6 months alone.
3.) Control - What happens if the exchange denies you access to the App?
4.) High Fees - Exchanges like HitBTC charges as much as 0.001 btc (approximately 7 USD at the time of writing)