You get an inbox notification for moderator elections on every site where you are able to vote for the candidates. According to the election page itself (yellow note on the right):
Any community member with 150 reputation may vote in the election.
So if you have enough points on SO to vote in the election, you of course get notified for it. How else would you be able to use your right to vote?
Regarding Ask Ubuntu, elections on different Stack Exchange sites are neither coordinated nor regular, they happen when there is a demand and the moderator team and/or Stack Exchange team decide to hold one. Reasons for that might be old moderators stepping down or a significant increase in moderating tasks due to site growth.
You didn't get notified of any Ask Ubuntu elections because currently there simply are none.
You also said you couldn't vote for any of the candidates on the current SO election because you don't know any of them. This is a valid problem, but the possible solutions are obvious:
Don't vote. This is the boring solution, but nobody forces you to vote.
If you don't care enough about that site, don't want to support any of the candidates or simply are not able or willing to invest the few minutes, just ignore the notification and move on. It's not exactly a really good solution, because every democracy relies on a high turnout of voters to be able to represent the community properly, but not voting is your good right just as much as voting.
Inform yourself about the candidates using the material provided on the election pages:
- the nomination statements and the comments and replies below those
- the candidate scores (x/40 points; where half of the score is determined by reputation and the other half by relevant moderation badges)
- the candidates' answers to the moderator questionnaire (links can usually be found as part of the nomination statement)
- the links to their regular user profile with all available general information and activities
This information should already give you a quick but pretty good impression on whether a candidate is rather suitable for the job in your opinion or not.
If you are able to invest more time, check out the candidates you deem acceptable in more detail. You can look at their activities like review actions or meta posts as well as regular main site participation or their behaviour in chats, if applicable.
Finally, the time span from beginning of the nominations to the end of the final voting stage is over two weeks. This is also still enough time to make contact with any candidate you're specifically interested in and ask questions.