Hey Forcedflesh, it's pretty much as Shannon mentioned. In designing our mice, we aim for the best balance for the largest user group. We also provide a variety of mice in different sensors / shapes / ergonomics to match.
With the THERON in particular: we looked at many mice on the market, and noticed some mice curved strongly on the back end making the length shorter & some were more gradual in curving, producing an elongated shape with a pronounced left side that jutted out (assuming it's a right handed mouse) .
Users generally fell into 2 categories, in regards to this curve:
[1] the gradual curve/elongated shape, seemed to be in the way when using a palm grip. feeling unnatural
these users would find a strong curve with a shorter mouse length to be a more ideal shape for palm grip.
[2] the gradual curve/elongated shape, was good as it made for a more secure palm grip.
these users would find a strong curve with shorter mouse length to feel "hollow" when using the palm grip. Because they expect something to be against their palm.
Thus with the THERON, we aimed for a middle ground, the mouse is not as long in length as some others but the slight angular emphasis can still give that 'secure' grip feeling to users whose preference more matched [2]; while also providing a back end shape that should not agitate 'as much' the users whose preference fell in [1].