I don't really know anything about photography, but I'd speculate that after smartphones became good enough for most amateur shutterbugs, lens makers were freed up to focus on people who were willing to accept extra mass for higher performance.
I, too, don't know much about photography beyond lugging my wife's lenses ;)
For example, a lot of early wide-angle designs (eg Biogon) were symmetric, and actually went into the throat of the camera, because if you had a 28mm lens, the nodal point was actually 28mm away from the film. That type of design went away when SLRs needed to put the mirror there, and we switched to lenses that are essentially "reverse telephotos" (the nodal point is farther away than the focal length). Modern lenses for digital cameras take this another step further and put the the nodal point at infinity, so all the rays of light are coming straight into the sensor at a 90 degree angle of incidence. However, since the lens must be a very strong reverse telephoto to accomplish this, it constrains the rest of the design and requires more elements to correct properly.
https://en.wikipedia.org/wiki/Telecentric_lens
https://en.wikipedia.org/wiki/Ang%C3%A9nieux_retrofocus
https://www.casualphotophile.com/2017/10/11/jupiter-12-35mm-...
I wonder wether the weight gain is based on the glas or the body. Are there more lenses with metal bodies to give them a luxury touch.
Both.
In the micro-4/3 system, there have been several "pro" level lenses released in the last 5-10 years. These tend to be both physically larger (to let in more light and allow faster fixed apertures) and all-metal construction. More actual glass, metal body that is physically larger = lens weighs substantially more than an equivalent focal length "kit" lens.
I too sold my Canon DSLR kit for Olympus. I rarely carried the Canon stuff because it was bulky. But, I still wanted a bit more flexibility than the compact 1" sensor offerings.