MPLS over GRE

Hi all

I was going through some GRE use cases and i found that MPLS runs over GRE.
I cant visualize any proper use case logic for this MPLS over GRE. And that
GRE is termed as soft GRE. Is there anyone who worked on MPLS over GRE
implementation. Where it is used extensively and how it is been designed

I can see that when SP is not offering MPLS services , then we can tunnel
over MPLs switched packets from ISP to other ISP over GRE where the latter
ISP support only IP and not MPLS . Is there any other scenario or else any
special use case for MPLS over GRE.

Thanks in advance,

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