Because Fred would hafta buy/lease/rent servers with storage capacity for all those uploaded images, and/or reconfigure TERB to actually hold masses of pix instead of just linking to them. He doesn't want to.
As was pointed out, no probs if you become the image server for your own pics: just get a permanent web-addy (that static IP, plus your own filename coding) you can identify the pic with, so the software can magically assemble it w/ yr post when some TERBian decides to read them. That, and leave your box on and connected to the Weeb 24/7. But you don't want to do that.
Fortunately there are image hosting/serving sites whose business is accepting your uploaded images, storing them with unique URLs so they can be linked and seamlessly assembled into other pages on demand. They want to do that.
You probably can load a pic right into the text of your message, BUT it would appear as miles if incomprehensible alphanumeric gloop and would vastly exceed the character capacity of a single post. Besides, to do that you'd hafta first get that code for the pic. It doesn't exist as an image y'know, your 'puter and its software knows to make an image when it sees that code handed off to it in expected ways. The BB software is not one of those ways, that software only knows how to handle links, not those big image codes. Best you should accept that magic it is, unless you're limited by its 'inadequacies'.
What's the diff to you, between uploading to an imagehost and uploading to Fred?