Why do calculator manufactures like to reinvent the wheel?

[Stefan]

The following is not really a complaint and also not really Prime specific. I am just curious and maybe someone of HP can answer this:
Why did HP choose to invent their own programming language (again)? Why not use something more established and still comparably easy like Python, Pascal, Ruby etc?
The Prime seems to be a device which has been designed pretty much from ground up, so compatibility to older calcs can't be the reason.
I would say performance shouldn't be an issue either, at least Python is pretty fast, especially with JIT.
The learning curve is also shallow for Python or Pascal.

So no real disadvantages I'd say.
Furthermore if one uses an established language like Python one has a big standard library which could be used, in case of Python even some pretty advanced numeric and symbolic libs. Plus a lot of developers would be already familiar with the language and even more important the standard library.

And as everybody can see this is not specific to HP. TI invented their own BASIC flavour (at least NSpire eventually included Lua scripting, however its not really advertised), Casio probably too has their own BASIC flavour. So where does this drive come from? Is there a secret codex among calculator manufactures "And you shall not covet your neighbor's programming language"? :-D

I hope for some enlightening comments by Tim or anybody else being deeper involved in the innards of calculators :-)