I can't speak much for other countries, but for the Germany I suspect that a big part of the difference ultimately derives from a different voting and representation system that is much less focused on individual politicians, and therefore has a much lower tendency to devolve into a popularity contest. (It's still a popularity contest, but much less so.)
The unit that really matters in Germany is the party, and the most important vote in all elections at the state and federal levels is a party vote rather than a vote for an individual. Something like a Sanders candidacy would be completely unthinkable in Germany simply because of how the elections work.
(There is a secondary vote in elections in which you vote for an individual, but that can only marginally affect the final composition of parliament in terms of number of seats per party. The details are complicated, and for the purpose of this discussion it's best to pretend that this secondary vote doesn't exist.)
At its most extreme, neither the chancellor nor the state prime ministers are elected by direct vote.
Then there's an admittedly somewhat random element of political culture in that there are no open primaries. The selection of candidates within each party is done by vote among delegates internal to the parties, and is almost completely devoid of public spectacle. (The news media typically reports once on these internal elections on the day that they happen, and that's it.)
To top it all off, parties are subsidized by the state. Once a party wins a number of votes in an election - the threshold is fairly low, and lower than the number of votes required to enter parliament - they receive money proportional to their electoral success. This reduces the need to create a huge fundraising apparatus in the first place.
I'd say Lessig is right in that campaign financing reform is probably the best path forward for the US, since changing the other aspects I mentioned would require much deeper constitutional changes.