@Gwen407
It's a real shame that there is such poor trust in customers.
There are websites dedicated to instructing guests how to scam free stays on Airbnb and this includes how to gather false evidence, doctor photos etc. It's not a rare occurrence and, one of the most popular scams involves claiming there were bed bugs (or other pests) or mould or hidden cameras or a gas leak. If successful, the scammer gets a free stay, but the consequences for a host can be much more severe than having to provide a refund (as @Anonymous has mentioned above).
I am not saying that you were doing this at all and I don't doubt you had a bad experience (I was once attacked by bed bugs whilst staying in a hostel and it was really horrendous), but of course, when a guest only reports the problem after the stay is completed, without having given the host a chance to address the issue, it can be a sign of someone scamming for a free stay. The timings of this made it difficult for both you and the host.
To say that Airbnb doesn't take these reports seriously is simply not true. You just have to browse this forum to see that they often have an extreme and knee-jerk reaction, suspending high standing hosts based on a claim from one guest without giving the host any chance to challenge that claim.
However, it is only natural that there should be some timescales and procedures in place for guests to report issues, just as there are procedures and timescales for hosts to report damages caused by guests and evidence needs to be provided. Otherwise, it would just be a free for all for scammers from both sides. There is no reason for Airbnb to simply take your word for it.
Also, considering the host doesn't have other reviews mentioning bedbugs, it's likely the previous guests introduced them to the apartment, something that was beyond his control. I'm not saying that's your problem, but I also don't see other reviewers mentioning mould or cleanliness issues or the other complaints in your review. It seems to me that the host has been punished enough as it looks like you really tanked his ratings.