Whether we like it or not, this is an established fact that ICOs have given more harm to investors then good. On daily basis, we are hearing news of an ICO scam in which people lost their money and there is no way to recover that money. This gave big tech an opportunity to ban ads related to cryptocurrency and ICOs.
Big tech (like facebook,twitter and google) fear not cryptocurrency nor ICOs but their underlying technology i.e. blockchain. On blockchain there are already platforms developed and successfully running that are a decentralized alternative to what google, facebook, and twitter are providing. By placing a ban, Big tech are trying to save their business which will cease to exists if blockchain based apps became a success.