Weakening the democracy through non-voting?
Vote for a different party, or vote for the same party. There are enough options available.
like Putin and Erdogan in power
Nope, because there were safeguards like this in both countries, and both leaders found ways to circumvent them. Putin simply made his puppet president for one term. Erdogan's party AKP had a rule preventing any politician from holding an office for more than 3 terms. Erdogan simply became president and changed the political system to his liking.
It makes sense to establish safeguards like this in immature democracies, or presidential democracies, but not in a highly federalized parliamentary democracy in which there are so many checks on the PMs/chancellors power.
Being a head of state for over 10 years
Well, Germany does have a term limit for its' head of state, the German president. The chancellor is the head of government.
Besides, at least in Germany, Adenauer, Kohl and Merkel received their 3rd terms for their remarkeable political achievements. Adenauer for rebuilding Germany, Kohl for reuniting Germany and Merkel for keeping the EU and Euro together.