Well, there are many attacks for both desktop and mobile devices, and I would certainly not consider a mobile device as more secure than desktop. You can lose a mobile device, it can more easily get stolen, there are wifi attacks over insecure networks, all sorts of apps require all sorts of intrusive permissions, and so on. The typical protections like drawing a shape or similar to unlock the device wouldn't stop someone from either brute-forcing into your device or simply disassembling it and reading from its disk.

And, as an additional point, if you really care about security, it's not like you can install clean Linux on a mobile device and install only software packages you know and have checked, so that you only have open-source software on your machine and you know what everything does and how it works. This kind of thing is standard if you operate a server. And you would encrypt any sensitive information like passwords, you wouldn't at all store them as plain text. I don't know how you can achieve any of this basic level of security on a mobile device.