There is few reasons:
1) to pay weekly dividends you need pay HIGH FEE like 50 ETH today it will rise with eth price
2) paying dividends you send money to lost accounts too
3) paying dividends you send money to exchanges BIG money for NOTHING it hurts investors
4) legal problems with paying dividends
5) someday exchange want delist token because law can change in favor classic tokens like in JAPAN there you can not trade "company share tokens"
6) weekly dividends would HURT market with loosing liquidity / traders would avoid playing with ICN
7) with buybacks more MONEY will add value to ICN price than just dividends no profit is lost.
8 ) ICN go for POLO now..
9) 8000BTC+ will be directly invested into ICN


Of course there are "-" too.

PS: Which token you would keep dividend or buyback ? Buyback one will have higher value IMO