I'm not sure what the reasoning is for the restriction, but it dates back to very early version of C3 according to our version control. Either it was to avoid a bug discovered during the development of C2, and hence C3 doesn't have any notes around it, or it was an arbitrary choice.
Interestingly 144 appears to be a reference sizing for the modern pt size, being exactly 2 inches in height.
Either way it appears if you use the "set font size" action it ignores the limit, and you can make your font as large as you want. If this value was chosen because of a bug, this might cause problems, but it appears to work for me.
Ashley might remember the reasoning.