Question: Why was this movie made-for-TV and never released theatrically?
Answer: Same reason why so-called "Home Alone 6" will appear on Disney+ as an original film - as explained previously. Although if Home Alone 4 was anything to go by, the bottom of the barrel was scraped to the point it had a hole in it. Patched I reckon by "Home Alone 5."
Answer: It's a separate movie set in the same universe, a sort of reboot. Introducing a new younger child to the franchise.
Answer: In addition to not being able to cast child star MacCulkin again (who drew earlier crowds but was now older and "not so cute"), the script was not of the same calibre. Without being able to surpass the previous highly successful HOME ALONE movies in quality and desirability (as well as meet fans' high expectations), it was a way to offer "something" (less satisfying but "cheaper" to produce) by going straight to TV or DVD (the next best thing).
This answer doesn't explain "Home Alone 3" though.
Question: What caused Finn and Alexis to become technophiles?
Answer: I'll provide a "response." This seemingly simple/ straightforward question has a straightforward answer as well as a complicated one. The simple answer is it is impossible for anyone to know with certainty what "caused" them to be or become anything. There are theoretical perspectives that may offer different possibilities. Scientifically, there can be factors that are associated/ correlated with being a technophile, but there can also be unknown factor (s) that contribute. The complicated answer would break down your question and not take it for granted: What do you mean by "technophile"? What criteria are used to define someone as a technophile? Is "enthusiasm" measurable? Do Finn or Alexis meet the criteria for a technophile? Is using a technology that is readily available because of the historical time in which one lives the same as being enthusiastic over new technology? Is an addiction or obsession the same as enthusiasm? What evidence do you have that they are technophiles, etc?
Both Wikipedia and Home Alone Wiki state that Finn and Alexis are technophiles.
Does either provide a definition of "technophile" or provide criteria or evidence?
Finn is obsessed with video games and Alexis is obsessed with listening to music via headphones.
Answer: Simple answer is because ABC Family along with Fox TV Studios produced the movie specifically for their television audience. Which is what they did for "Home Alone 4" as well. Airing original movies on a channel is a way for networks to increase ad revenue as it draws an audience to watch their movies. They wouldn't have a need (and probably not a budget) to release it in theaters.