They had a great run for decades of course. They decided nobody would want a computer on their desk at home. 
They tried to play catch up but it was too late as 10+ major PC/software manufacturers invaded. Crashed with everything else in the tech bubble. They had a decent run after the financial crisis and that was it. They have tried some M&A. If you can't run a huge business and grow it organically, the merger thing usually goes bad. Similar story for other large companies that were once revered. GE,T,PFE etc. in decades long struggles. Paying a good dividend (until they don't), because nobody would stick around otherwise. I don't know if IBM has done many spin offs yet but that might be next if they don't get things working before the next recession. Sometimes just getting much smaller is the last attempt at doing something beyond surviving.
They tried to play catch up but it was too late as 10+ major PC/software manufacturers invaded. Crashed with everything else in the tech bubble. They had a decent run after the financial crisis and that was it. They have tried some M&A. If you can't run a huge business and grow it organically, the merger thing usually goes bad. Similar story for other large companies that were once revered. GE,T,PFE etc. in decades long struggles. Paying a good dividend (until they don't), because nobody would stick around otherwise. I don't know if IBM has done many spin offs yet but that might be next if they don't get things working before the next recession. Sometimes just getting much smaller is the last attempt at doing something beyond surviving.