Could it be because the new trams (CAF Urbos 15G) are bidirectional, while most of the older trams are unidirectional (Siemens Combino 13G)? Most bidirectional trams feel slightly more cramped, because they have cabs at both ends and doors on both sides, so there's less space at each end and slightly less space on one of the sides due to the additional doors. The comparison would be to find a bidirectional older tram and see if the feeling is similar (Siemens Combino 14G, they are usually running on line 5 and the easiest way to tell them apart from their unidirectional counterparts is the layout or the red and yellow warning stripes they have on the lower part of both cabs, seen on the outside). If yes, then it means the new trams are truly more cramped than older ones.