In the deuterocanonical Trek Litverse (specifically the eBook The Insolence of Office), in addition to what Andrew mentioned in his answer, it was because of security concerns as described here. To summarize, following the events of Generations in which his VISOR was hacked and used to aid in the destruction of the Enterprise-D, and coupled with the previous incident of VISOR-based brainwashing in The Mind's Eye, La Forge was ordered by Admiral Hayes (of various screen appearances) to replace his VISOR as a security risk or be reassigned to a less-sensitive post.

In the deuterocanonical Trek Litverse (specifically The Insolence of Office) it was because of security concerns following the events of Generations in which his VISOR was hacked and used to aid in the destruction of the Enterprise-D, and coupled with the previous incident of VISOR-based brainwashing in The Mind's Eye.

La Forge was ordered by Admiral Hayes (of various screen appearances) to replace his VISOR as a security risk or be reassigned to a less-sensitive post.

La Forge was tempted to tell the admiral that, no, he wouldn’t pardon the expression. But he restrained himself, and said instead, “Sir, I have had this VISOR for over thirty years. It’s a part of who I am. You can’t force me to give it up.” “No, Mr. La Forge, I can’t force you,” Hayes said. “However, should you elect not to comply with Starfleet’s current security standards, you would not be able to continue to serve aboard the Enterprise.”