Why would hosting change apparently improve rankings?

[JudgeJeffries]

I recently changed hosting for a very old website and suddenly its performing well again which it used to do in the past having slipped dramatically a few years ago to the extent that I had just about given up the ghost.
My question is whether or not a change in host could have made such a huge difference and what are the possible reasons for that difference. I had thought it may be due to a rival website being hosted on the same server and being given preference in the serps or perhaps a penalty on the server.
Any suggestions on this matter would be appreciated.

[austtr]

Not sure if this case matches your situation.... but a few years ago I read comments that claimed a country specific website should be hosted in that same country. At the time I had a Florida site hosted on servers here in Australia.

I changed to a USA located host and there was a very definite improvement in traffic numbers.... no significant change in rankings for the trophy terms so I'd say the improvement came via long tail searches.

Make of that what you will. No guarantees given or implied.

[tedster]

Here are some ideas:

A technically flawed DNS set-up gets corrected

The new hosting is nearer to an Internet backbone is faster

The new hosting gives faster access to your site instead of sharing so much with others

Better crawling because of better server/database response time

You dropped away from some kind of hidden hack during the move
(some of today's hacks are insidious, and they only inject hidden links, not malware)

No "bad neighbors" on the IP address (essentially the same idea as the opening post)