The answer lies in the ''I'' at the beginning of the word. In Thai, a short sharp ''I'' is a derogatory way of describing somebody. If you didn't like me, for example, you can call me ''I-Andrew'' with a scowl, though not to my face because it's very rude. I am guessing Ikea sounds like a rude way of referring to a person by the name of ''Kea''.
But some companies have fared a lot worse in the name-mangling stakes. Volvo, for instance:
First, there is no ''v'' in Thai, so they replace it with a ''w''. Second, the final sound of a syllable in Thai cannot end in ''l'', so ''Vol'' becomes ''Wonn''. And so Volvo becomes Wonn-wor.Thai is, actually, a language with a very different phonology from English so pronunciation is hard in both directions. My Thai friends are too polite to laugh at me when I try to do it, but they can't quite hide their amusement.