It’s not in the bible because the principle of tzniut was part of the culture which Jesus did not contravene — except when the Father hitched his robe to run to his prodigal son who was returning.
The reason it’s been a recent phenomenon in our present culture is that it is only since the 50s that the 2nd sexual revolution took off all the morals and clothing of society.
However, the issue is that men have not been open and transparent but have imposed rules to cover their shame. Instead of saying — I’m really sorry but I’m struggling to talk to you without noticing your cleavage please could you help me out — they say “cover up” and put the shame on the women.
Yes women are free to wear anything “but not everything is beneficial” for us men who are wired visually.
Yes we men must take responsibility and I certainly pray about this (see my blog post on “how to stop looking at women lustfully”) but I’d rather not put my head in the lions mouth and then pray to God for it to not bite me.
So on my journey out of sexual dysfunction I will be blessed by those ladies who help me see them and who who they are and not their cleavage as that is too easily a stumbling block to me.
And I’ve found by being vulnerable and honest about my struggles, ladies have been so gracious and loving by removing this stumbling block. And I too reciprocate by helping them in their struggles.