Why does the office market Staples sell Montblanc refills, cartridges and ink bottles but no Montblanc writing instruments?

Staples carried years ago, at least in Hamburg, also Montblanc writing instruments, which were offered as a discounter under the RRP. Thereupon Montblanc stopped, according to reports in the Hamburger Abendblatt, the supply of writing instruments. Refills, cartridges and ink continue to be carried, because Montblanc itself maintains an own online refill shop and the distribution of consumables is less strongly regulated. Montblanc refills also fit some writing instruments of other manufacturers (e.g. David Oscarson or Caran d'Ache), while Montblanc ink cartridges are proprietary.