Bluebird couple makes retreat!

Finally after 3 years of struggles, it appears we will witness the growth of the bluebird population. Can't wait!
Three years ago I put a bluebird house up on a tree post. It was up about 5 feet, what is recommended from what I've read. Each year we had bluebirds build their nest but something (raccoons, other birds???) interfered with the process.  This year as usual the bluebirds came, built their nest, laid their eggs and again something got into it. I promptly took the  tree post out, bought a 10 foot pipe, cut off two feet (actually my dad did that for me... Thanks dad), painted it black, added a guard (I'm having a senior moment... What's that guard called? Ah yes, its called a baffle) Then put the house back up. Two days later bluebirds were back, building another nest. They are 7 days into the incubation period.  Another 7 or so and there will be little featherless babies screaming for food.  Now the next hurdle is keeping Indiana (the family kitty) away from the fledglings.

After all the trouble I've had, it makes me wonder why they recommended putting a house up on a tree or wooden post?  No wonder they were endangered.