Austerity performed for gaining recognition, adoration and propitiation, exhibiting pomp and ostentation, is regarded here as rājasa, and is unstable and fleeting.
The mind in general is quite shallow, extrovert and trivial. It is averse to think about leading a qualitative life of real enrichment and elevation. At the same time, it has a flair for gaining popular esteem. Thus it gives in to pettiness and ostentation. With a view to winning esteem in the eyes of others, it takes to religious austerity. So the real aim and focus of austerity gets lost.
The rājasa nature looks for pomp and flamboyance, to become noticeable to people around. That leads to hankering after special welcome and adoration from others, acclaiming whatever is being done.
A dignified human way is to be humble, quiet and unassuming, especially while performing worship and austerity. Only then will the performance be effective and bestow the desired purity. Rājasa instigations are calamitous. Pride and pomp dominate even their religious austerities or spiritual practices, and bring downfall.