why does apple removed iphone x, xs, xs Max from the "apple.com"?

Yes. They have stopped making and selling those models. The iPhone X was removed in 2018, when the XS and Xs max were released.

Apple does not keep an ever existing list of past models on sale. They change available models when they release new ones.

houssam ~ "...the iPhone XS can be picked up in 64GB, 256GB, and 512GB storage configurations for $899, $1,049, and $1,249, respectively. Likewise, the iPhone XS Max can be had in the same storage configurations for $999, $1,149, and $1,349. The only catch here, as noted by Macrumors, is that you'll have to head into an Apple Store to make your purchase." Source:

Apple shaves $100 off iPhone XS lineup following iPhone 11 announcement

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You will have to contact a store to see if they still have any in stock. You can't get one from apple.com any more.

houssam32 wrote: "Is there any specific reasons?"

houssam ~ We don't know as we're just users. And besides, from the ASC Use Agreement:

"...do not add Submissions about non technical topics, including:

(...)

Discussions of Apple policies or procedures or speculation on Apple decisions."

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You can still buy them third-party. Check your local electronics store or Amazon.