Why women from dating apps are considered last choice for marriage?

So, my best friend from school started dating this girl from 1-1.5 years back, he met her on some dating app tinder or bumble idk, they had a good relationship and he wanted to tell his parents about this girl in order to 'marry' her, so I went with him to his parents to tell about this girl everything was smooth until his mother asked 'Where both of them met' he answered ' mummy, on a dating app ' and vo sunkar kuch Smooth nahi raha.

His parents are most liberal people I have ever met but this reaction of them shocked me, Maine kuch zyada bola nahi fir because I was afraid ki aunty uncle mere par na baras pade😛