Speculation: Before GPS POS, possibly on a different type or even manufacturer, TOGA selections re-sets the FMS position to runway threshold coordinates.
That's what the T. O. Shift is there for on the mainstay A320 PERF TKOF page. Even today.
This position update could be essential for achieving long-range navigation accuracy outside radio coverage, going trans-Atlantic for instance.
Perhaps carried over from legacy operations / procedure commonality purposes?
It could well be a requirement for NAT and guess they do some MFF.