ICQ was a classic first mover that had explosive growth and continued to succeed in a relative way, but not relative to the overall market. AIM, Yahoo! and MSN messenger platforms knocked it off that pedestal, and the company seemed more interested in sabotaging its platform to squeeze ad revenue than making it more relevant or meaningful to their userbase.

I think they let the product fade because they weren't making very much money. It hard to have a vibrant product when you can't pay the rent.

MSN messenger and Yahoo both had significant funds.

They had funds from their parent companies which made money by other means. I'm not certain, but I suspect neither product made any money for Microsoft or Yahoo. What CEO in that position is going to double down on R&D funding to keep the chat program relevant?