>Why you want to reduce value of creative work, but not a value of other assets?
The framing isn't charitable. People want to weaken copyright because it is a government granted monopoly. There are negative economic effects (i.e., for everyone) to government granted monopolies. Other assets generally aren't government granted monopolies.
Owning the copyright to a work grants the exclusive right to profit off that work, but so does owning a house grant the exclusive right to profit off that house. House ownership is not a monopoly because there are other houses, and you can build a new one if there's sufficient demand to justify the cost. Similarly, copyright ownership is not a monopoly because there are other copyrighted works, and you can make a new one if there's sufficient demand to justify the cost.
The negative economic effects of monopolies stem from a lack of competition leading to insufficient supply, but there's no lack of competition or insufficient supply of copyrighted works. Even if copyright were indefinite like other property rights, it wouldn't stymie the supply of new works, but rather expand investment due to raising the future expected profit.
> copyright ownership is not a monopoly because there are other copyrighted works
they are not fungible, unlike houses.
Also, if you could copy a house like you could copy digital goods (i would download a car), i am also going to claim that the "monopoly" on the house must also be shortened.
Sure, there are idiosyncratic preferences and some people really want that one famous work, but there are also idiosyncratic preferences when it comes to houses, and particularly famous houses command a premium, but that doesn't render houses nonfungible. For most people, any house they enjoy living in will do, and any content they enjoy consuming will do.
You would download a house or a car, but the people making new houses or cars would only offer them for download if they can charge enough for each copy to make back their original investment. So houses and cars could be expected to cost about as much as a movie ticket or book or game. That those are currently much cheaper is also an indication that competition is successfully working to drive down prices close to the cost of production.