Lots of people have been asking this throughout the game community. Here's the explanation from the C-Ops community Discord server:

Yes unfortunately it’s true. On Monday the 10th of July 2017 we need to shut down the PC version in order for us to concentrate on the mobile version.

Originally when the company was founded the first game from the company was Critical Strike Portable of which the first version of was for the web browser. But many years ago the company founder Veli-Pekka was at GamesCom in Germany to showcase new game ideas and the game idea that got the best response was Critical Strike Portable for the mobile platform.

There wasn’t much PC or console-like games on the mobile platform at that time – nor is there that many now either. It made total sense to target the platform with less competition. Thus the decision was made a long time ago that the company focus was going to be mobile from that point on.

All this lead to Critical Ops being created much later on with mobile focus. We did keep the PC version of Critical Ops around at the beginning because it was convenient for testing purposes and in any case the deployments were at that time very similar to mobile deployments so it wasn’t that much of a hassle. But over time continuing to develop both the PC version and the mobile version became exceedingly arduous because the control scheme for the PC was so radically different and the whole feel of the game was so much different on the PC than for the mobile platforms.

In addition to that during the last couple of years many browsers stopped supporting the Unity plugin that the PC version relied on. That meant we needed to go for Facebook Gameroom. Unfortunately there is not much players on the Facebook Gameroom platform. This also means that however the PC gamers that play the game are very vocal in the community there are way less PC gamers playing Critical Ops than there are mobile gamers. This is important to understand to see why we decided to cancel the PC version.

To sum it up: Critical Ops for the PC was not that popular in the first place and it required massive resources to continue to develop. We just can’t afford to keep the PC version around. It was a hard decision.

~ Critical Force's response

And there you have it.