I think it's due to a few factors.. the main factor perhaps being the mighty dollar. There are more obese people who are looking to lose weight and have the mentality that cardio equipment is the only and best way, when in fact they should incorporate a weight training program. Obese people will always be a client, whether it's because they decided to make a change, or their doctor told them they have to do it. Next, there are people who are slim who wish to stay slim and toned, so cardio is their thing. Even though they may use the free weights in the gym at times, they have weights at home that will suffice. Also, many women in general do not use the free weights and almost always use cardio equipment. Then of course there are people who are working to build muscle.. They still need the cardio machines for the obvious reason and also to help regulate body fat and make those muscles look even better. In a nutshell, pretty much everyone will use the cardio equipment and not everyone is using the weight training equipment. So, in order to keep clients and get new clients, they try to provide more of what the majority of people are using. The idea is that the usage of the weight benches can be figured out amongst those who are using them. In general, when the the gym gets too packed, it's left up to the members to figure it out. Some might choose to leave, change schedules, or not come. To the gym sales associates, it doesn't matter because more than likely the member is already locked into a contract. If the member doesnt come, it's ok. They can solve their space issue and get paid as well. They will probably get 5 new members for every one contract that's not renewed anyway.
Another factor is that many gyms are more so FITNESS centers. That's great, however not for the "body builder/power lifter". Things like.. grunting, yelling, chalking, are not really wanted and certainly not encouraged. lol. However they don't wish to discourage people who are looking to build.. that's why they let the dumbbells go above 100lbs. So, they put in moooore cardio equipment and just enough weight training equipment to satisfy lifters, not to make them happy. ( I would say to feed, not fatten.. but that's not a good word right now.)
Another factor is that people use the cardio equipment for a longer amount of time than people use weight benches. The average person might use the cardio machine for 20-30 minutes. Many will do 45mins-1hour. But the time spent on a bench is probably about.. 5 - 8 minutes.. at the most 10. So, it would make more sense to them to provide more cardio equipment because their is a longer amont of time between users.