Where does this pattern of naming products come from?

Solution 1:

This is more a question of psychology than etymology.

The resonance of X as a signifier of mysterious precision explains why it’s so common in commerce and branding. The Jaguar X-Type. The 2008 Mitsubishi Evolution X. The X2000, Sweden’s high-speed train. The X-Acto knife. Mac OS X. The X game for Nintendo’s Game Boy. Microsoft’s Xbox console. Vitamin Water XXX (with three antioxidants). The X is a California roller coaster (the seats swivel around). Product X is a protein powder for bodybuilders. The X-Vest adds weight for exercise.

Article in Psychology Today, with copious references and links:

What's So Fascinating About the Letter "X"?

Solution 2:

X is often used to abreviate a word that starts the with the "ex" sound like "extended","expanded","extreme" etc. or to represent the number 10 (roman numeral) , or words starting in cross (shape of the letter X)

• Lexus GX (Grand Crossover)
• IBM PC/XT (extended technnology)
• MX record (mail exchanger)