It's crazy. I guess part of the reasoning was that Clark wasn't Superman yet and he wasn't supposed to meet all those important characters that he meets at a later time(nevermind that him and Lex essentially grew up together on that show). That was the reason they only allowed them to use Bart and not Barry or Wally as their version of The Flash, and only in condition that he was going to be called Impulse and not Flash or Kid Flash. Later on when Clark started working at the Daily Planet with Lois and they started bringing in the big villains like Brainiac and Doomsday, DC seemingly eased up on the restrictions. That seemed evident to me when they brought in Supergirl, the Legion of Super-Heroes and the JSA. They brought in Darkseid for the final season ffs. Smallville could have Darkseid but Batwoman can't have Poison Ivy for more than 3 episodes? DC seems to have gone back to be just as ridiculous now as they were in the 2000s.