You might be wondering why your mouse cursor is titled at this weird angle? Like almost every other thing in the world and particularly, in the realm of technology and the internet; the mouse cursor too was designed this way for a particular reason. As stated in a document dated to year 1981, the reason for the arrow shaped mouse cursor and its leaning design has been presented here.
However, with the passage of time, it seems that there is no need for the mouse to remain slanted at a particular angle anymore. But given the fact that it was designed this way, it has emerged much as a standard in modern times. In earlier times however, when digital displays were still in their infancy stage, the cursor had to be designed in an angled display form in order to solve a major design problem.
The same was explained by software developer Bart Gijssens stating that when the mouse was first invented back in the year 1981, initial design included an arrow which pointed directly upwards. The mouse was first invented by Xerox engineer Douglas Enlglebart. Given the low resolution and poor quality displays of those times, it became difficult for designers to make out a tiny vertical line on the screen. Hence, when machines were finally made by Xerox and its research and development unit, Palo Alto Research Center (PARC); it was Englebart who decided that the arrow should be shifted to an angle of 45 degrees in order to improve visibility.
This allows the mouse pointer to become easily visible from pixilated background. The idea was soon borrowed by Steve Jobs and later on by Bill Gates, and since then left-leaning pointer has become the norm.