The humans of this world had no issue that Spark couldn't solve.
Want air to breathe? Use Spark. Want to eat and drink? Use Spark. Want to create clothes? Use Spark. Want to fly in Space? Use Spark.
There was nothing in this world that they couldn't do with Spark.
And that brought on a severe lack of growth to the entire human race. There was nothing they had to do to continue to improve. They could just use Spark.
The things that they used in their everyday life, the things that they were very useful to them were actually something that they kept around from a time in the past.
The things they used could be called copies of relics from the past. All they were were a crude imitation of the real stuff, made real by the use of Conversion.
Hell, these people had copied entire Spaceships and made it real using Conversion. They went the extra length to not have to do anything to make it work in some other way.
