Well, web games weren't necessarily meant to be overtly complex. Nowadays everyone is using engines programming in C++ or C# at the least. What's nice is that cross browser compatibility of these engines are being seen on the web in .io games which are all multiplayer games. Web games are not dead by any means, and game developers are now making more and more real-time multiplayer games for the web. However, if we are strictly talking about HTML5 games with no multiplayer aspect, then yeah I do think that market is "dying" but that doesn't mean you cannot make a successful HTML5 game. Web technology has gotten so much stronger which allows developers to make games more suitable for modern technology. Like TheBoneJarmer has said, there are also libraries like PixiJS and phaser that becoming more and more popular.