is that they have their superstar driver in whom they invest 30-50 million a year and feel the need to protect, so they hire a second-tier driver that can’t himself put on a proper run for championship
Are you high?
They had Lewis and Nico fighting it out for 3-4 years, they renewed both of their contracts during their battling. They signed Bottas as he was the best option when Nico surprised everyone and decided to retire after winning in 2016. Last year he did a very good job and managed to out qualify Lewis a few times and even win three races, which considering the late switch and the sudden huge step up in pressure and environment from Williams, was very impressive.
When Mercedes resigned him for next year they did so when the team was working well together and Bottas was doing well, while Mercedes once again found themselves on the back foot in terms of raw performance.
He could/should have won Bahrain, China and Baku and followed those strong finishes with two 2nd places before Canada. He then got taken out by Vettel at France, destroying half of his car a mechanical DNF at Austria, which he was running well at (I think leading?) and then a solid result at Silverstone.
Up that that point his season had looked solid, he'd been unlucky and perhaps lacks the self confidence he needs but at the point in which they resigned him he looked the best option. He was fast, reliable and worked well in the team. At the time non-of the 'top-tier' drivers were available, bar Alonso, which wasn't ever going to happen.
I’m so glad that actually Ferrari of all teams went for it and hired Charles next year, maybe it will force Merc’s hand to actuallly take some risks with their driver selection
I think this has more to do with the lack of faith they have in Sebastian to be able to beat Lewis. They have given Seb everything he wanted, more power within the team, more money than Red Bull ever offered him, a compliant team mate he likes and the best car on the grid. Yet Lewis is still beating him and still faster than him.
I see 2019 going for Ferrari like 2007 went for Mclaren, I can't see Lewis being challenged by Ferrari anymore now than he already is.