The NOVA filesystem/Patches from large companies

The biggest reasons why contributions from large companies have an easier time getting merged is that they tend to approach the kernel community with complete implementations that have been run for months on a large number of systems, and they often have benchmarks to show performance, memory, etc. improvements over a range of configurations. Compare that with someone who has a notion that they've tested a few times and seems to work for them.

Additionally, large companies tend to have the resources to hire people and keep them working on the kernel. This allows a level of familiarity and comfort with their work to grow. This is very useful when evaluating the likelihood that someone's work is correct, though the same factors risk a sense of complacency.

Note that that large companies do not always get it right. For example, multiple features Google created were too narrowly focused on Android and did not work as the larger community would have wished. It's taken years to remedy the ones that could be remedied. A large part of this was a failure to openly and frequently engage with the kernel community up front.

I would, however, hope that nobody is discouraged if they don't work for a large company. Those companies, economic powerhouses though they may be, tend towards group think and hold no monopolies on creativity. It's a lot of work to get something into the kernel but it still remains well within the abilities of lone developers.