surface boundary shrinkage after remeshing

[xiaolong7]

Hello, I tried the isotropic remeshing algorithm (tri_size_adapt=0, tri_shape_adapt=0) on a surface mesh with boundary and found that the surface boundary shrinks after remeshing, as shown in the below screenshot. Do you have any idea why that happened? Is there any way to preserve the original surface boundary as much as possible? Thank you!