It's a speciality of the Tornado tables which are mostly used in the US. It was introduced as a cost saving measure, because four additional figures are cheaper than a curved playing surface.
The curved corners in a traditional
table are of course necessary to avoid the ball being dead in the corners. With three players you don't need a curved corner and can still always get the ball.
There is actually a quite interesting documentary out there which tells the rise and fall of foosball in the US which is tightly coupled with the company behind the Tornado tables if I remember correctly. I saw it on Youtube a while a ago, but could not find it now. Might have been "Foosballers" but I am nit sure.
That's just the Leonhart. There are a number of other manufacturers that are approved for various types of tournaments including Tornado, which is most common in US tournaments and has a 3-man goalie bar.
There are quite a few tables that are considered tournament grade by the various table soccer associations, including ITSF (I think at least six manufacturers at this point?). In the US, Tornado is the most common tournament table by far and has a 3-man goalie bar, but many European tables like Bonzini or Garlando have the 1-man and raised corners.
The single goalie w the corner ramps was a late 1970s into the 80s things. Those are now less common as some competive foosball uses the three man rear, but there is one or more exceptions. I did the researh for my coed fraternity reunion, very hard to find the classic ramp tables, as they were made of particle board and degrade. The one company w ramps uses a more gentle slope rather than an added steep corner ramp.
Are there always three players in the goalie position? I seem to remember playing with one goalie (1-2-5-3 players), but that’s a while ago.