I sit behind a keyboard, mouse, monitor, and an incredibly powerful desktop operating system for 99% of the working day. These devices are pretty much the pinnacle of human-computer interaction; arguably the best tools we have for interacting with digital content with speed and efficiency.
But as soon as I want to do something involving my phone, I have to physically reach for it and immediately hamper myself with its limited UI, screen size, and ludicrously locked-down ecosystem limitations.
Smartphones have been around for decades and yet we're still nowhere close to seamless integration with the rest of our devices. The best we've got are clunky half-featured workarounds (Airdroid) or overly-complex techy solutions inaccessible to laypeople (VNC).
As another commenter said, it's all very much intentional. It's a deliberate choice on behalf of greedy phone manufacturers and greedy app developers. And it's really, really frustrating.