In Jain Dharma, Navkar Mantra is indeed the highest and most revered mantra. It is not a mantra of asking worldly favors; it is a mantra of salutation, remembrance, and purification.

If a guru maharaj gives other mantras, it is usually because those mantras are used for specific purposes, such as:

• Stuti or bhakti of a particular Tirthankar, Arihant, Siddha, or deity
• Daily spiritual practice for concentration
• Protection of mind from distractions
• Support in sadhana, vrat, or puja
• Following a traditional method used in a specific sect or lineage

So the reason is not that those mantras are greater than Navkar Mantra. Rather, Navkar Mantra is supreme in essence, and other mantras are generally secondary tools used for particular devotional or practical purposes.

The main understanding is:

• Navkar Mantra = the root, the topmost, universal salutation in Jainism
• Other mantras = auxiliary prayers or practices, depending on tradition and need

Important point:

A true Jain guru will never consider any mantra higher than Navkar Mantra. If other mantras are given, they are usually meant as supporting spiritual practices, not replacements.

Simple conclusion:

Navkar Mantra remains the most important mantra in Jainism. Other mantras may be given only as helpful additions, not as superior to Navkar Mantra.

If you want, I can also explain this from the view of Digambar and Shwetambar traditions.