A typical manufacturer approach is to beat the hell out of your suppliers on price to make your margin which is likely most of what Samsung does with its buying power. Apple does that but is also willing to throw money at issues and go as far as financing facilities for vendors. Where most manufacturers don't care about the device they sold the second it's out of warranty[1], Apple takes a longer term view of the relationship. So Apple is far more likely to say 'we need this fixed and are willing to provide X million dollars and a team of our own engineers to solve the problem' while Samsung probably goes more like 'make cheaper and make it better... and make it cheaper!'
So the reason Samsung typically has less influence is that when all you do is crush your suppliers margins to make your own, said suppliers don't tend to make much of an investment in making things better since they are incentivized to just make them cheaper.
[1] in fairness, they can't afford to: while Apple has an ongoing revenue stream from its devices, most other manufacturers don't. It's Google/Facebook/etc who monetize the devices post-sale while for the original device manufacturer it's merely a liability at that point. This is a factor in why Android has a rather dismal track record re: updates on older devices.
So the reason Samsung typically has less influence is that when all you do is crush your suppliers margins to make your own, said suppliers don't tend to make much of an investment in making things better since they are incentivized to just make them cheaper.
[1] in fairness, they can't afford to: while Apple has an ongoing revenue stream from its devices, most other manufacturers don't. It's Google/Facebook/etc who monetize the devices post-sale while for the original device manufacturer it's merely a liability at that point. This is a factor in why Android has a rather dismal track record re: updates on older devices.