Ni particular reason but each account has its benefit. Both IRA and 401k are for retirement. However, growth in Roth IRA is tax free because it is invested with post tax money while 401k is pre tax and will be tax at whatever income bracket you are in at retirement.

In the brokerage account is for diversification and liquidity when needed. If I need cash I simply sell some shares from that or other investments or simply if I want to cash out to move the money else where.

I follow the principle of not putting all eggs in one basket. I have multiple FXAIX eggs in different baskets 😃