the mark vi was the first saxophone to addressed the right saxophone design:
key mechanism, key placement/spacing, weight, neck design and etc...making the mark vi very ergonomical
and very comfortable to the sax player. sax players immediately went into the bandwagon bought the mark vi replacing their current horn.
therefore, the mark vi became the standard design for upcoming saxophone of other brands (i.e yamaha 62).
some saxophone brands were late to adapt to the mark vi design. selmer was reaping the success of mark vi.
effective marketing strategy (print ads) and selmer endorsement during the time also help promote mark vi as the best saxophone.
now, some (if not all) brands are based on the mark vi design (i.e. yamaha, yanisigawa, keilwerth, p mariat).
selmer even released the reference 54 as based on the mark vi design.
the mark vi design improvements (print ad).
john coltrane was a selmer endorser (print ad).
currently, the mark vi is considered the "holy grail" of sax musicians.
all of these contributed to the success of mark vi as the choice of saxophone of all sax musician.