For Y Combinator startups, the average Series A is 5x larger than in 2008
mattermark.com
mattermark.com
That's not how moving averages work. You can't just take an unordered univariate and smooth it however you want.
You argue in your first chart that time is a relevant factor; therefore, you must smooth as a time series for that analysis to make any sense. (which wouldn't make sense in this case anyways, due to the nonconsistancy in timing of seed funding.)
Also, the annotations in the first chart make absolutely no sense since they are not relevant in any way. (unless you are asserting that correlation of these events implies the causation of the increase, which is very bad logic unless you have proof otherwise)
Regarding annotations in the 1st chart, they are to set context for readers who do not necessarily follow major milestones in the private markets landscape.
There are many other contributory factors in the raising of a Series A and why the amount has increased over the years, one major one of which is the fact that the US economy has vastly improved since the Great Recession of 2008 and investor confidence has rebounded. (notice the huge dip in the year of 2008)
Chart annotations usually indicate events which have a causal, identifiable effect on the data that the user would otherwise question as odd without an explination, which is why adding the annotations only confuses your point.
As for the trend itself, it's probably due to overall market trends, and the increasing prestige and network effects YC companies receive as the number of them increase.
Graph: https://twitter.com/DanielleMorrill/status/49357608066654208...