Plot3D: why certain part of the plot is excluded?

Here is a simple 3D plot, but some part of the plot is excluded.

wq[k_, xe_] := Max[ 90 xe - k, -5]
Plot3D[ wq[k, xe] , {k, 0, 50}, {xe, 0, 0.5}]
Plot3D[ wq[k, xe] , {k, 0, 50}, {xe, 0, 0.5}, Exclusions -> None,
PlotPoints -> 100]


Although I can fix the problem by using Exclusions->None, I am still puzzled by why there is such a large gap in the original plot. In fact, my original plot range was very small, and the entire surface was excluded-- I got an empty plot. I spent hours looking for errors and finally realized that I was plotting an excluded area. Could any expert explain how exclusion area is determined in Mathematica? Why such a large area is excluded in such a simple plot? Thank you so much.

• no such problem in V 12 in windows 10. screen shot !Mathematica graphics – Nasser Sep 3 at 17:32
• This is strange. When I run it again, now the gap shows up! May be it was a chance first time it worked. !Mathematica graphics. But if you add Exclusions -> "Singularities" to first plot, then it becomes OK. Look at help for Exclusions – Nasser Sep 3 at 17:40