Lox, a linear progression does not mean no rise.
A mathematically perfect one (y=mx+c) would give an identical increase for each time period.
Real life situations are never exactly perfect, but it is remarkable how good this one is.
The points are closely packed around a line of best fit with an annual increase of about 120.

I am open to challenge on everything I say, but I would be surprised if anyone can shoot me down on this one.
That is a linear rise.
Of course it could change, become exponential or reverse.
We can only look at the evidence and speculate.
WHO and UNAIDS have done that and we have seen their conclusions.