Back in the eighties and before, manufacturers would design and produce engines in small displacement. Off the top of my head, International made a 155 and 179 three cylinder engine, 206, 239, and 268 , plus a 239 turbo engine, and 310, 358, 402, and 358 turbo six cylinder engines, all the same family, and all made on the same line.
Deere had a similar lineup.
The complexity and logistics were mind boggling, and very expensive.
Today, manufacturers understand the cost of this complexity, and, with modern electronic common rail fuel systems, can offer one basic bore and stroke in three, four, and six cylinder versions, and cover the same power range.
Remember, the manufacturer is selling power. Without the different displacements, it was easy to buy the lowest power engine, and turn the pump up, cutting the manufacturers profit.
With modern electronics, it’s not so easy.
Remember, although we all like cheap tractors, the manufacturer needs profit to develop new products and keep investors happy.
Without profit, it’s a race to the bottom.