I assume there is some misunderstanding on my part about the vaccine-creation-process and which factors play a role in it. Below is my current understanding.
Toxoplasmosis is a disease that can infect both humans and cats. It doesn't have a lot of symptoms, i.e. if you have it, you might not even notice. After you have had it, you are immune to further infection because your body has toxoplasmosis-antibodies now.
Toxoplasmosis is dangerous in one situation: if a pregnant woman gets it, it may cause disabilities in the baby (even at later ages when he/she grows up) or even abortion. This can only happen if the woman has not had the disease earlier in life, because then she would be immune. (It's also dangerous for people with a weakened immune system, such as hiv-patients, but you can't vaccinate them anyway so let's disregard them for this question.)
Vaccines are weakened or dead virusses/microbes that cause a certain disease. The body recognises them as a threat, makes the appropriate antibodies and remembers these antibodies in case it encounters this disease again. When the non-weakened disease shows up, the body doesn't need the time to invent/create the antibodies anymore, so it can start to destroy the disease before it becomes too strong.
This only works for diseases for which your body can invent antibodies (given enough time), for which it will remember the antibodies and for which the pathogens don't evolve fast.
Why is there no toxoplasmosis-vaccine available? It seems toxoplasmosis is an ideal vaccine-candidate: the body can create antibodies and will remember them. The pathogen doesn't even need to be dead or weakened, since the symptoms for the disease are so low. It seems to me that this vaccine would be "just" inserting the toxoplasmosis-germs into the patients blood.
I'm thinking about a vaccine for women who are not pregnant. Obviously inserting the disease into already pregnant women is a bad idea.
Possibilities that I thought of:
The toxoplasmosis is caused by a parasite, which may be too big of a difference with virusses/mirobes to create a vaccine out of? But why would that be harder?
Toxoplasmosis may have annoying pathogens, that don't want to survive and reproduce in a lab, so you'd have to hunt the parasites down in "the wild" for every vaccine, which doesn't seem to be feasible.
Something causes such a vaccine to be too expensive for the hasstle.
Nobody wants to fund research to create such a vaccine, because other diseases are more dangerous.
Related question: Why are some viruses harder to make vaccines for? but this question asks for all possible reasons why a vaccine can not be created. I'm interested specifically in toxoplasmosis.