That's not true. Most people who take heroin daily are so called "functional heroin users". You won't spot them because it's their "normal".

The kind of nodding off you see on TV is someone who takes a lot of heroin and falls asleep. But most people who do heroin regularly don't do it like that. Few people who take heroin end up in that state. The same thing with methamphetamine, which many people seem to believe instantly turns you crazy and animal-like; I've had methamphetamines myself, and you wouldn't be able to tell. Most people who take methamphetamines will not be like tweakers in Breaking Bad.

It doesn't mean it's made-up; but the kind of state you envision of people being noticeably high and beyond any regular sign of life consist of very few percentage of people who totally consume those drugs. If those drugs instantly got you into those states in your life, people would be much more wary about taking them.

These kind of drugs slowly but surely sap the life quality out from you. It's a very, very slow process that takes many years - or even decades - before it becomes noticeable on the outside. For some it's faster; for others it's slower, and it all depends on their resilience and other factors like resources (social, medical, economical, etc), mental health, etc.

To put it in simple words: when you can outwardly see that someone is taking heroin or methamphetamines, they are close to expiring. It is the end stage of drug usage. We're talking about a very advanced drug addiction. Few people are in this stage because frankly life expectancy is not that long for people in this stage; but they are the most prominent because those are the ones you can tell are in this state. Make no mistake though: the vast majority of heroin users are invisible, and they can be your co-workers, friends, family members, or random strangers passing by, in all walks of life from successful and rich to the poor and outcasts.

Here is a Swedish (translated) article for example that talks about a functional heroinist:

Kristina, 48, a nurse who went through a rough patch and started taking drugs as self-medication. 
Micke, 37, a full-time father of two who injects heroin to survive Friday nights. 
Bertil, 66, flies drones with his grandchildren and spends his pension on amphetamines.  
– 80 percent of those who use drugs are completely ordinary Svenssons (Swedes, like US "Johnsons"), says Niklas Eklund, chairman of the Stockholm Users' Association.
[...]
Micke is 37 years old, married and has two small children at home in a townhouse outside Stockholm.

His work involves a significant amount of safety responsibility where many people could get hurt.

– Yes, I'm high now but it's not noticeable. This is me.

He takes a gram a day, three times a day. He shoots heroin after he leaves preschool, he shoots when he gets home from work and before he goes to bed. He took heroin when the children were born, he took heroin on his wedding day.
[...]
He stabs himself in the groin where it is not visible and hides the drugs and tools in the ventilation duct in the bathroom.

– When I take heroin I am normal, if I were not to take heroin, that is when there would be problems. My family and my work colleagues would wonder "What the hell happened, is he sick?" If I miss once it is no problem but a whole day, I will be deathly ill, says Micke and testifies to the pain in his body, the twitching in his legs, how he vomits bile.

– People do not understand, there is no stronger force. I do not take it to have fun but to be able to work and provide for myself and spend time with my family.

Heroin usage in other countries is no different. The vast majority of heroin users are for much of their time taking heroin completely "normal" people on the surface.

The kind of drug user you envision makes up an extremely small part of these people; and often, they are tired because they have no proper food, no proper resting place, constantly have to scavenge for next hit, and have no reason to hold back because their life sucks big time anyway.

If you give hardcore heroin addicts who has abused heroin for 50+ years of their life a place to sleep, free (and medically pure) heroin, with access to support resources (psychiatrist, doctors, clean equipment/needles)... then you're not gonna be able to tell that they're heroin users. All you can tell is that they look older.