Nobody knew how much McLaren would steamroller the entire field in 1988. While it was clear that Senna was the centre of attention at Lotus, it wasn't clear how far behind they were. Senna had finished a good 3rd in the tables in 87 and was never far off the pace in 86 or 87. With Williams relegated to the Judd V8 they were destined to be noncompetitive in 1988. McLaren had been using the TAG engine for some years and nobody could have known that switching to Honda would work so well in their first year together. They had also gone off the boil in 1987. So it was logical for Piquet to assume that Lotus Honda would give him a good chance. He'd have the undisputed best engine, a clear #2 as a team mate, in a team which had experience with Honda and perhaps some favours for running a Japanese driver.
As it turned out, Senna had been flattering poor Lotus cars, and the team was in terminal decline. But at the time that was far from clear. The 1988 car had many problems, which Piquet and Nakajima kept telling the team about but they were unable to solve them. IIRC Jackie Stewart tested it after the season ended and agreed with Messrs Piquet and Nakajima.
Edited by absinthedude, 06 August 2020 - 15:36.