It's my understanding that
A) The providers of the actual ring did install "Separate" fiber for
SFTI but I have no idea whether or not they're in new rights of way -
I'm willing to bet not
B) Reducing the points of entry into the ring reduces complexity and
makes it much easier to recover the ring in the event of a disaster.
Understanding that SIAC has thousands and thouands of customers
connecting at the DS-3+ level to get data that's generated from one
place means that you need to keep the distribution uniform. Basically,
it boils down to them being able to say "Our ring is up, if your
connectivity to our ring is down it's your problem" in order to maintain
fairness between Trading firm A that has 10 people and Trading firm B
that has 10,000 people.
When they were maintaining separate interfaces for each customer they
could potentially run into issues where they'd get certain larger firms
back able to trade sooner than smaller ones and then you create unfair
market disadvantages.