McLaren split with engine supplier Renault over a disagreement about Formula 1 strategy, according to Cyril Abiteboul.
"It was apparent that Renault and McLaren have different ambitions for the future," he said.
The Renault team boss was speaking after it was announced at Sochi that McLaren will switch to customer Mercedes power in 2021.
Abiteboul explained: "McLaren and us are fighting for fourth place.
"We both have the goal to close the gap to the top teams. In our opinion, this would have been a faster process with a strategic partnership, with the motto: together we are stronger.
"But McLaren did not show a great appetite for that," the Frenchman added.
The development means Renault might not have a single customer team in 2021, while Mercedes has Racing Point, McLaren and Williams.
"It's a missed opportunity," Abiteboul said. "But only an arrangement like that (with McLaren) would have made sense for us.
"The downside is that we will get less data."
It is now rumoured that Williams could be forced to switch to Renault for 2021, as the current rules limit each engine supplier to just three customer teams.
But Mercedes' Toto Wolff seems happy with four Mercedes-powered teams on the grid.
"More customers, more data," he said.
"We already noticed that in 2015 and 2016, when we had four teams with Force India, Williams and Manor."
Abiteboul explained to Auto Motor und Sport: "We are differently set up to Mercedes.
"They build everything themselves in Brixworth, but most of our parts are made externally. We then sell the engine to the customer under FIA rules. We make no money from engines."
One rumour is that Renault could push to secure at least one customer team, but Abiteboul insisted: "We will not force anything.
"We would only do something with another team as part of a strategic partnership."
McLaren supremo Zak Brown said of the decision to switch to Mercedes: "We will compete with the best engine against the best team. Only if we do a perfect job we will be able to beat them."
Wolff smiles: "That's the only risk of the deal."
Brown said McLaren will continue to build its own gearbox, and retain full political independence.
Wolff said: "That was never our goal. Our customers are free to decide according to their interests.
"We only talk to them when it comes to questions about engine regulations."
