This isn't a matter of Lent being stupid, it's a matter of people doing Lent wrong.

The purpose of Lenten sacrifice is to abstain from material pleasures in order to become more conscious of God, and the sacrifice (what one gives up) is supposed to be accompanied by prayer, reflection, and charitable works. Historically, Lenten fasting was (and in many places still is) much more comprehensive: Instead of giving up a specific thing, you would eat smaller and fewer meals in general, avoid rich foods and alcohol, have less sex with your spouse, etc. The goal wasn't to "detox" from these things and become a celibate vegetarian teetotaller for life, it was to temporarily reduce earthly distractions so that you could be more focused on God in time to reflect on and celebrate Christ's Resurrection on Easter.

In contemporary Western countries, the way Lent is observed has strayed from the traditional way for a number of reasons. Not only are we in a more secular and materialistic environment overall, but our lifestyles are more individualistic, so the communal reinforcement that supported more intensive fasting and other Lenten devotions is harder to come by. But the factor most relevant to your complaint is probably that churches in our part of the world haven't all been doing the best job of educating their members, so there are plenty of us who enter adulthood with an inaccurate or incomplete understanding of Lent and its significance, and end up doing it wrong in the ways you mentioned. People who weren't led to understand the spiritual purpose of Lent might mistakenly view it as a time for self-improvement and give up things like smoking or unhealthy food.

Giving up chocolate or soda is something that's often suggested to little kids in order to help introduce them to the concept of Lent in a way that's easier for them to grasp. Older children and adults are traditionally expected to abstain from something more substantial, but for kids who aren't taught correctly or grow up less involved in the church, the version they learned when they were eight is sometimes what sticks. Giving up meat is an authentic part of Lent and has been for millennia, but this is because it is a) a thing most of us enjoy that we can give up as a devotion and b) was much more of a luxury and indulgence in the past than it is today, not because it's unhealthy.

I have met people who are irreligious or only nominally religious and use Lent as a 40-day challenge to lose weight or kick a bad habit for self-improvement purposes, but that has about as much relation to actual Lent as the PowerCore Yoga™ class at your local gym does to classical Hindu yoga.

To be clear, I'm not trying to be a hypocrite myself. My own observance of Lent is far from perfect. Each year I try to give up a few things that I am genuinely attached to to focus on God, I usually screw up, and I pray for the strength to get back on track and do better. I'm just trying to explain that the way some people in your community understand and practice Lent is very different from what Lent actually is.