We are lucky to have found the Antikythera Mechanism.
According to Sprague de Camp, in his book, The Ancient Engineers, some of the temples did make use of mechanical devices to impress the worshippers.
It could well be that the Antikythera Mechanism was the best one built. Even then it didn't survive very well. The metals used could have been severely lacking in corrosion resistance. Other, less expensive models could have been made out of even less durable material, maybe even wood. Even now our technological brilliance can sometimes be limited to the aspirations of a single person. Nowadays we can almost manufacture Galileos and Da Vincis, but back then I would say they were few and far between. If you had something that made you a big success the idea of sharing its secrets probably was not going to happen.
Global population estimates, both the number of estimates and population numbers for that period are also very sparse in number, could be 150 million people. There was probably only a few countries where hard science was extensively practiced. The social grouping was distinctly pyramid shaped, with few at the the top and slavery a commonplace position in life. Possibly one third of the Roman population in big cities was slave status. Outside of the big cities anywhere there were large peasant populations. That had to limit the quantity of cool stuff.
With any product, it has a procedure for proceeding through time, that involves it either fading away or becoming so popular that some form of it can always be found. As it starts to travel through time one of the things that can happen is cannibalizing of its parts, either because they can be used for something else, or they look really cool. The pyramids were covered with fine stone work. All of that has disappeared, taken down and used for other projects. Early in their paths to the future engineering instruments were probably always collectible for any number of reasons, falling into private hands and then disappearing. After a country's fall from power it probably wasn't unusual for things that represented that country's success to be trashed.