Indeed, the reason hedonic and imputed values are added to the GDP - together about $6 trillion - or a spare Japan - is to keep the debt/GDP near 100%.
Or maybe it's because (in the case of imputed) we need to quantify the value of someone owning their home and living in it. Consider that if everyone owned a home, but rented it to someone else (and rented a home for themselves with the proceeds) , you would have the exact same situation as if everyone just lived in their own home. Except that without imputed value the latter would contribute nothing to GDP, while the former would contribute massively.
To remove the (artificial) fluctuations from people switching from ownership to renting, we just calculate it as if everyone was renting.
In the end all that really matters is that you calculate GDP consistently from year to year - and including hedonic and imputed values makes our measurements more consistent. All that matters is the trend.