Why is Merz so heavily favored by the betting markets? Ignorance, too much emphasis on polls of the public or...?
Depending on the betting market and its participants there can be a lot of wishful thinking involved. Merz is certainly not a Trumpist but rather some kind of Reaganite who is popular with people that are nostalgic of a more ideologically pure CDU like it was in the opposition years (1998-2005). It's quite likely that more ideologically oriented people are more engaged in the betting markets in the first place.
Is it due to the digital vote? (no "peer pressure" to vote for an establishment candidate). I'd imagine CDU delegates were extremely "vanilla" and establishmentarian. Merz got close last time, but now they're way ahead so "why rock the boat" and risk losing centrist voters by going right. Doesnt really make sense to me.
Merz is not anti-establishment in every sense of the word. It's just that many members and leading figures think that times have moved on. But he and the direction he represents remain popular with many in the CDU.
I don't know about the party researcher, but I will say why Merz might have a chance. I think that when AKK ran for the first time she had governed the Saarland for several years; but it's only the Saarland and apart from that she was mostly an unknown entity and seen as representing a continuation of Merkel's course. Laschet and Röttgen (and to mention all relevant persons Spahn and Söder) are all known entities.
Laschet is moderate, jovial and well-connected, but during the COVID-19 crisis he has become unpopular with the core of lockdown fanatics for seemingly being too laissez-faire.
Röttgen lost the 2012 election in NRW and was demoted from Minister of Environment by Merkel afterwards, which would play well in the story of a candidate like Merz but makes a more consense-oriented candidate like Röttgen look like a doormat.
In the end it is not said that the non-Merz vote will converge on a single candidate.