The market overall is growing faster than Apple’s market.
Example: 100 people bought smartphones yesterday, and Apple sold 14 of them. They have 14%.
Today, 110 people bought smartphones, and Apple sold 15 of them. They now have 13.6% of the market share. Even though they sold more absolute numbers.
Tomorrow, 130 people will by smartphones, and Apple will sell 16 of them. They now have 12.3% of the market.
In each case, Apple’s absolute sales are increasing, but their share of the market is dropping. Essentially, the market is growing faster than Apple’s share of it.
I thought it was rather intuitive - absolute sales and market share are not the same thing.
Now relate that to only appealing to their base. The part of your initial post I’m actually contesting.