A lot of this has to do with your general health, activity level, metabolism, and what else you expose yourself to.
Your body can and does process and eliminate things from your system on a regular basis, and the small amount of lead from shooting would be hard to measure on someone that is physically active, has a good diet, and does not do something for a living that exposes them to toxins.
The same person working as a blue collar worker in heavy industry though may already be exposed to toxins including heavy metals, have less income for or make poor decisions about their diet, and probably gets rewarded with overtime that means they have little life outside of work doing things that remove as many toxins as they spend hours adding them.
These things are accumulative, and accumulating them faster than you can remove them from your organs and bones happens more readily if your body is also trying to remove other heavy metals or toxins.
Being a heavy drinker or on prescription or other drugs that occupy or reduce how readily your liver and kidneys filter your system also would make it harmful at a quicker pace.
Your body does a lot of its repairs and flushes out toxins during sleep, so your sleep becomes a big factor too. It takes many hours of sleeping in a row to remove a lot of waste products, and cutting into your sleep means you are carrying over toxins from one day into the next and accumulating them.
You absorb very little lead if it is not in dust form, being breathed in, or eaten that way. If you are not eating, or smoking, during shooting, or casting your own bullets in the fumes of lead between washing up then you likely will need to have other habits in life for regular shooting to add enough lead to your system faster than it is removed by your system.
Some parts of the nation are more toxic, have had heavy industry longer than people cared about the pollution it causes, and Trump did just about destroy the EPA so I am sure some places are pouring toxins into your environment that pose significantly greater risks than the minor lead from shooting does.
Other people work in industry where there is fumes or high exposure to raw materials on a regular basis.
Currently the solid waste of sewage processing is being used as fertilizer for our food crops, this includes all the the drugs, metals, and chemicals flushed down a toilet or dumped down the drain by big industry, and which is poorly dealt with by a sewage treatment system that primarily eliminates living things such as bacteria, viruses, and parasites, rather than removing toxins such as metals, drugs, or other chemicals.
This means you are exposed to all the drugs and chemicals that go down a toilet each time you eat, and probably adds far more toxins to your system than shooting ever will.