Why do some market makers have many Market Participant Identifiers (MPIDs)?

I noticed that some (most?) market making firms have many Market Participant Identifiers (MPIDs). For example, from the list of NASDAQ market participants¹:

• "Jane Street Capital, LLC" has the following MPIDs: JANE, JNST, JSAP, JSCA, JSCT, JSJX, JSML.
• "Virtu Americas LLC" has the following MPIDs: ALTX, DTTX, GFLO, ITGF, ITGG, ITGI, ITGP, KCGB, KCGC, KCGM, NITC, NITE, VALD, VALR, VALX, VIRT, VNMS, VRTU.

I observe the same pattern with other firms such as Cantor Fitzgerald & Co., GTS Securities LLC, Citadel Securities LLC, etc.

I’m aware that some of the MPIDs for Virtu can be attributed to acquisitions of other market making firms (e.g. KCG Holdings, Inc., Investment Technology Group, Inc., etc.), but what about the rest of its MPIDs? If not mistaken, Jane Street has not made any acquisitions of market making firms. Why does it have so many MPIDs?

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¹ ftp://ftp.nasdaqtrader.com/symboldirectory/mpidlist.txt