The original Lois & Clark aired in the 1990s. These are the X-Files years where Chris Carter simply ignored the issue of sex regarding his main characters for six plus seasons. And it worked!
On the other hand, sex was a major topic in popular culture. Just about every 1980s-early-90s sitcom had THAT episode, the one where the teenager decides to have sex and the parents have to prove how supportive and non-judgmental they are. For that matter, the 80s/90s were also the years when well-meaning adults got nutty about labels. LGBTQ teens were supposed to come out as some kind of message to the universe and a boost to their own self-esteem, a forced confessional that I criticize here (as do many M/M writers).
The topic is still omnipresent but not as frantically discussed. Some people will claim that this is because teens having sex/people having sex before marriage has become too much of a norm. The truth is, the number of teens engaging in sex has decreased in the last ten years. In fact, Castle took for granted that Alexis would wait until college. And while that was far less likely with Mandy from Last Man Standing, there was no corresponding pressure placed on Eve to "grow up right now." (Not that any guy without massive self-confidence would mess with Eve anyway--see above image.)
Sex is no longer being used as a coming-of-age ritual, not to the same degree as it was thirty plus years ago.
Still, in television world, if two adults with no religious upbringing don't sleep together before getting married or moving in together, the question of "Why?" arises. What's the background?
My background for Lorry and Clark is as follows:
Lorry, somewhat more than Clark, was a geeky guy in high school. He came out in college at the same time that he grew several inches and got downright good-looking. However, he has never fully accepted that he is an attractive guy.
Lorry has great insecurity about relationships, which was compounded in college by the Linda King episode (see "The Rival" from Season 1). Lorry was dating a confused guy whom Linda stole away. This event is one reason Lorry is so definite about never dating a guy who isn't totally and completely 100% out. He is wary with Clark, whom he doesn't entirely trust until the end of Season 3. And he is tired of having his heart stomped all over. He has more sexual experience in some ways than Clark but that experience is fairly limited.
In many ways, Clark has a much broader view and understanding of sexuality than Lorry. Although he didn't come out to his parents until moving to Metropolis, he traveled a great deal after college and consequently had experiences that actually make Lorry look a tad naive--which is something of a staggering revelation to Lorry who has to readjust his image of Clark as the naive country boy (Clark is--and isn't).
So Clark and Lorry are cautious, which doesn't preclude other approaches. But cautious. Which keeps the timeline intact and makes it possible to put off the episode "Soul Mates" until the fourth season.