Why is snuggling or nursing an older baby or toddler to sleep considered a hle and a problem?

It depends on how tired she is. She's always been nursed to sleep (she turned 1 this week), normally it takes 10-30 minutes, but in the last few days it's been longer, more like an hour, I guess it's because she just mastered walking and added so many new words to her own language, sleeping must be really boring for her now:) The only time I saw it as a "problem" was on Tuesday, and that's because my ear infection has returned for the third time in 2 months, I had a very busy and tiring day at work and I generally felt crap. After almost an hour and half of trying to get her to sleep I was close to tears. But normally I enjoy every minute I can spend with her, be it play-time or nursing to sleep, probably because I work full time and don't see her as much as I would want to. Sorry for the long story:)