Hasn't real movie production always been inaccessible at Uni? This is nothing new.
Actually no, in fact, if you go back to the LONG history of Universal Studios Hollywood and the beginning (1915 - 1930), Carl Lamelle (founder) charged admission and a box lunch for a nickel to watch filming, but when they stopped silent productions and went to adding sound, they had to stop that due to needing to keep the area quiet. But for those years, the crowd would cheer for the Hero and Boo the Villain, and the actors loved the added atmosphere to get into character even more.
Then in 1964, the "modern" version of the Tram Tour started, and I remember going multiple times as a kid.
The way it was set up, you paid admission and got in the queue to board a tram, and then made multiple stops including some designed for the guests, such as special effects and make up demonstrations. At the end of the tour, you exited to an area that was shops and restaurants.
In the early years, they added better tour stops (you got off the tram, walked to the few stages used for the tour as a group and then re-boarded a tram as part of the same Group (though it might have been a different tram), a break area (Prop Plaza), which everyone got off the tram and had access to restrooms, shops and a quick service restaurant on the upper level, and then got back in the queue to become part of a new group for the second half of the tour. This allowed the tour to be longer, and give folks a break (and a chance to get into their wallets). Also, since the tour was ALWAYS first, the exit area (now called the upper lot) could open later in the day, and help with labor costs. Also, the first main stop is now the current lower lot, and the building that is now Transformers hosted two main stages, first as two separate shows, then converted to the same show on each stage to increase capacity.
The upper lot grew with a museum, and more shops and restaurants and photo ops. I remember the vending machines that would make a "hot wax" statue right in front of you as a kid for about $1, loved doing that. Also, they had a cheesy Snow Effect (Snow flakes coming out of a squirrel cage) that was a good photo op. Then the upper lot grew with show venues and more photos ops and entertainment.
Well, Universal found they were maxing out the capacity of the tram tour, so we got the first form of FastPass in the industry. Now, most folks were still sent to the Tram Tour first, but on very busy days, they would have the Upper Lot open early, and then hand out return time vouchers to ride the tram later in the day, to keep the main queue waits down, and increase total capacity for the day.
Today, it is the VIP Experience at Universal that gets you the backstage access, as part of its long tram tour, you do get to make stops along the way and get out and explore (the main tour is a one-stop tour that lasts about 1 hour). The VIP tour will allow you to tour a working Studio set (but not actively filming),I have been on the Voice Stage just before the season one year, and they made sure no photos were taken, but they also have done other stages, it depends on what is available. And stop is Six Points (western area), and even allowed to enter some of the buildings, many of which were built as working sets and not facades decades ago.
The Property Department is also a regular stop, where you can walk around the actual warehouse.
The War of the Worlds set is also a regular stop where you can walk the area.
So it is still available, but at the higher price, but similar to what WB offers for there most expensive tour that also comes with a meal.
And yes, Paramount does offer tours to guests.
And then nobody has mentioned Sony, which also does tours in Culver City, and is popular for those Jeopardy/Wheel of Fortune fans. Alas, weekdays only.
I would rate them
Universal VIP, since you get the same basic experience as Paramount and WB for the same price, but it includes the Theme Park and Front of the Line access inside the Theme Park)
Paramount VIP, then the other two Paramount options (regular and after dark)
Sony, due to its limited amount of some unique things in a historic location.
The WB, opting for the Deluxe (What Universal and Paramount call VIP), and then the "VIP" (aka regular) tour.
I don't like the WB tour for the main reason, they make you lock up your cameras during most of the tour.