Monolithic, calcified thinking in the medical profession
plus
highly likely the USA/UK tested out biological weapons in the Outback, as they did with nuclear and chemical weapons, and have ever since been determined to keep all their dirty little secrets and screw ups, covered up, regardless of actual reality, just ANYTHING that might be related they will stamp down on.
Lyme fits right in with the NATO Cold War bioweapon doctrine:
make folk sick for long period,
don't be obvious,
don't kill in huge numbers,
very hard to treat and deal with, and especially make it near impossible to categorize AS a bioweapon attack
ruin the enemy's manufacturing/infrastructure/command personnel (military are much harder to harm due to awareness of NBC weapons etc and NATO viewed destroying enemy's ability to create war materiel as better use of weapons of mass destruction),
don't do anything to obvious/excess that would provoke M.A.D. response.
So they invested heavily in diseases that ruined crops, livestock and sickened people rather than out right killed them
And also remember that a lot of dirty stupid things go on because no one has bothered to find out the reality!!
there MAY have been orders to quash information about things like Lyme in the past, but it may have been temporary and no one bothered to change the rules, to inform them
or that it's just FEARED by some idiot politician who had quiet orders to hush things spread, without even bothering to get really informed by the scientists working on such projects!
for example, very silly thing in British army (WW1 or 2 era) was that they had two guys standing to one side of each artillery piece, well one person investigating how to improve artillery, finally got around ot asking WHY the hell they were standing there doing nothing?
it was because they were the men who once held the horses when the guns were pulled by horses
and no one had ever thought in the years after horses were replaced by trucks, to change this stupid bloody order to have two men stand off to one side doing fak all rather than serve the gun!
moral of that story being to show a lot of stupid crap goes on.