Why does the rule of investigation (Taharri) for mixed garments differ from that of vessels?

Choosing Correctly among Mixed Utensils and Garments (التحري)

• Because garments are physically larger and easier to clean.
• Because Wudu with water has a legal substitute (Tayammum), whereas covering the body with clothes has no legal substitute.
• Because garments are always considered inherently pure in Shariah.
• Because vessels are made of clay or glass.