bugcat: As a player myself stuck in the wall, I wanted to offer some thoughts.
The 5k Wall is the third of four rank barriers noted in player data and extensively referred to in the Go community: at 13k, 9k, 5k and shodan. The precise ranks at which these walls occur depends on the system of the server or federation, but the level of playing strength is similar wherever.
With that said, what are the causes of the Wall preventing players from easily passing 5k? Here are some of my ideas.
1. It's just numbers. Since 5k tends to be the roughly average rank, it should be surprising that cresting the hump is difficult.
2. Satisfaction / complacency. This idea, alluded to by strong OGS player and amateur Go writer Mark5000, is that many 5ks believe that they're in the top quartile: that they're "good" rather than, as said, average. Having attained a "good" rank, they no longer feel the incentive to improve.
3. Aptitude. There's no denying that some people take more readily to Go. It can be suggested that strong Go players are often also particularly skilled at mathematics, music, medicine, language learning and other board games. Talent exists, and perhaps 5k marks the distinction between talented and untalented players.
4. Wealth and teaching. When one reaches the Wall, it will become clear that the availability of free reviews, commentaries and lessons has become sparser. To continue receiving teaching of a sufficient standard to improve, it might be necessary to become a customer of a commercial organisation such as the NGD, the AYD or so on; or else pay a professional like Michael Redmond for teaching games. This would suggest that low income players will struggle to pass 5k. Travel and accomodation costs to visit tournaments and congresses are another feature in support of this theory.
5. Failing to play stronger opponents. If one mainly creates open game challenges with no handicap, they will often be taken by weaker players and those of the same level as you. And it is important to play down and across the pool, of course, but not to excess. Making a game offer with handicap may be better at drawing stronger players in for an interesting game; players who dislike to take handicap might, then, find it harder to reach stronger opponents. Facing better players is a key part of improvement.
6. Not reviewing one's games.
7. Not counting.
8. Not doing tsumego. It is at the 5k Wall that many players first become serious solvers of tsumego, since their reading skills require improvement. It was once difficult to access large quantities of tsumego, but 101Weiqi has made this easier.
9. Careless time management. Especially needlessly slow play in the opening. At this level, a time lead of ten minutes is arguably worth more than even a five point gain in fuseki.
10. The language barrier. Players with linguistic access to Oriental materials in Chinese, Japanese and Korean will have a larger sphere of content to choose from.
11. Excessive copyright. Almost all books relevant to breaking through the 5k Wall are held in long periods of copyright. For instance, even if John Fairbairn passed away this year, his 1968 translation of Sakata's Modern Joseki and Fuseki would not be released into the public domain until 2092, 134 years after publication. In comparison, Honinbo Shuho published Hoen Shimpo 139 years ago, in 1882. How absurd would it be for Hoen Shimpo to still be a copyrighted work, and how could a modern player hope to learn from it on its eventual emergence?
tapir: Lack of money can certainly make everything (in life) harder, but you live in the fortunate age, where you can download a professional level opponent for endless teaching games and reviews for free or a modest one-time fee. That you start lacking opponents at 5k already is probably due to the go server you play on. The other things you miss out on, don't even have that much of an impact on your playing strength. Go congresses, tournaments are all nice if you are invested and want to immerse yourself in the community, but I don't believe they translate to strength in a meaningful way. (And yes, I consider it bad form to speculate on the death of an elderly, but very much alive author.) If the investment into a small amount of books (you don't need a large book collection to become a better player) is causing you trouble already, you are probably at a point in life were you should consider your priorities. I.e. a more stable financial situation (looking for a /better paid/ job, qualification, cutting superfluous expenses etc.) would serve you better than spending your spare time and beyond into volunteer work and Go immersion.
See also GettingOutOfASlump