Probably because it’s likely not a genuine Vacheron Constantin, unfortunately. The closest thing this resembles is the Royal Eagle (chronograph, not the day-date), but there are a number of differences between this and the real thing that should be noted:

1. The real Royal Eagle chronograph has a “big date” complication near the top of the dial, whereas this has a date window at 4:30.
2. The font on the subdials is wrong here. Note that the subdial numbers on the genuine watch are much larger than they are here.
3. The watch in this post has Roman numeral hour indices, whereas all of the genuine chronographs have regular numerals. The only example of a Roman numeral Royal Eagle was this day-date.
4. The Royal Eagle chronographs all have a minute track running along the outer edge of the dial. The watch in this post does not.
5. The subdial functions on the watch here are different from those on the genuine Royal Eagle chronographs. At 9 o’clock the genuine chronograph’s subdial is a 12-hour subdial, whereas here it appears to either be a 60-minute subdial. At 3 o’clock, the genuine chronograph has a 30-minute subdial whereas here it appears to be a 24-hour (AM-PM) subdial. The 6 o’clock subdial appears to be a typical 60-seconds subdial on both this watch and the genuine chronograph.