Alphabet blocks - how do they choose the letters?

Asked one maker & got no response, so maybe you all know - how do they decide, in chidrens’ blocks, what letters go together on a block. Is it random, something to do with letters that don’t need to be put together to make many words little ones will be learning to spell, or what?

Was going through my old stuff and I just wondered.

I’m doing a little googling to see if I can find anything, and I came across this. Presumably, each block has only one letter, so there’s no decision to make. One letter per block, and you’re done. But I’ll try to find a different set somewhere. I think the ones I used to have were like you described: multiple letters on each block.

I think that’s the point; all the blocks I’ve seen have six different letters per block, but not the same six letters on any particular block (the same individual letter may appear on several blocks though).

I can’t imagine that it is completely random though, as they must have to tool up to make these things.