Very simple: some factory made emulsions contain hardeners which prevent the bleaching and the creation of a matrix necessary for inking.
Some liquid emulsions don't have hardeners in it. There's a little known Foma liquid emulsion that does not contain any hardeners inside (you can add it separately, for ordinary silver gelatin prints). Unfortunately, Foma does not export this product outside the Czech Republic. (If they changed their mind and they do now, please let me know... it's also veeery cheap and glossy too!)
I have yet to experiment with Adox/Efke. I got this emulsion and have used it for normal bw printing. It's not as good as SE1 or Foma. Dries up quickly and I don't like it's contrast.
Most of the liquid emulsion I tried (Maco, SE1 and another brand which I don't remember) do not work for bromoil. I don't think it was Tetenal. You could give it a try: coat your paper with emulsion as you would do normally. Print your photograph, fix, wash, wait until dry, then bleach and see what happen. If it doesn't bleach correctly it won't work. Sometimes it apparently bleaches ok, but then in the inking stage turns out as a mess.
Then of course, you can manufacture your own emulsion. Most of the recipes found in the "Silver Gelatin" book will work. Emulsion making can be as hard as making a successful bromoil. Many formulas required a lot of dedication and a darkroom optimized for it. I have been successful only in preparing the simplest one but it had to be used straight away from preparation.