Yeps that a good point but i guess thats how life is all about... Like for parents and siblings we don't tell them we love them or express our love to them because they know we love them. You have like a blood relationship with them, we often take them for granted because we know they will always be here for us and this is how life is.
But in romantic relationship like BF, we tell them 'I Love You' everyday because thats how it is, its like u meet them later in life, ur the one who is forming the relationship and must keep it alive till the end because there is no familial bond that bind them, it all depend on love.
Whereas for family, parents and sibling, u have a bond with them.. Like for example ur parents does not tell u I love u everyday, and it does not really matter because u know that they love u and they don't have to say that, there action prove it whereas id ur BF/GF does not say I love u one day then it mean he/she does not love u.. Well i guess thats how love is.. U can never actually explain it..