It might be because a lot of people tend to not distinguish between ‘feeling’ and ‘emotion’—considereing ‘feeling’ as an exact synonym for ‘emotion.’
While not necessarily easy to explain, emotions are mental occurrences that have specific labels, of which everyone probably has experienced at one time in their life. They are purely an emotional reaction to a physical or non-physical event. Examples of emotions are: anger, jealousy, fear, love/infatuation, shame, guilt, joy, etc.
Feelings, on the other hand, is anything that can be felt, and more often then not is an involuntary reaction, usually due to an external source (compared to subjective and oftentimes due to an internal source for emotions). A good example of a feeling is pain, which is in no way an emotion; or stress, exhaustion, disbelief, doubt and… dukkha (which is painful feeling). 
The PTS Pāli-English Dictionary also translates vedanā as ‘sensation,’ which is quite accurate.
Vedanā (f.) [fr. ved°: see vedeti; cp. Epic Sk. vedanā] feeling, sensation (see on term, e. g. Cpd. 14 Mrs. Rh. D. B. Psy., ch. iv.) D i.45; ii.58 (cp. Dial. ii.54), 66; iii.58, 77, 221, 228, 238 (°upādāna); S iii.86 sq.; A i.39, 122, 141; ii.79, 198, 256; iii.245 sq., 450; iv.301, 385; Kh iii. (tisso v.); Sn 435, 529, 739, 1111; Nd1 109; Nd2 551 (tisso v.); Ps i.6, 50 sq., 145 sq., 153 sq.; ii.109 sq., 181 sq.; Vbh 135 sq., 294, 401, 403 sq.; Dhs 3, 1348; Nett 27, 65 sq.; 83, 123, 126; Tikp 246, 317 sq., 345 sq.; Vism 460 sq.; DA i.125; VbhA 13 sq., 39 sq., 80, 178, 193, 221 (°ânupassanā, in detail), 263 sq., 382 (various). — Three modes of feeling (usually understood whenever mention is made of “tisso vedanā”): sukhā (pleasant), dukkhā (painful) adukkha-m-asukhā (indifferent) […]
Soucre: PTS Pāli-English Dictionary