The Gemara in Pesachim 113b (according to the girsa of Tosfos) states:
שבעה מנודין לשמים אלו הן יהודי שאין לו אשה ושיש לו אשה ואין לו בנים
ומי שיש לו בנים ואין מגדלן לתלמוד תורה ומי שאין לו תפילין בראשו
ותפילין בזרועו וציצית בבגדו ומזוזה בפתחו והמונע מנעלים מרגליו ויש
אומרים אף מי שאין מיסב בסעודת (בגמ׳: בחבורה) מצוה
Tosfos Pesachim 113b:
ואין מיסב בסעודת מצוה - היינו סעודת מילה, דאמר במדרש דניצול מדינה של
גיהנם וסעודת נישואין בת"ח ובת כהן לכהן
According to Tosfos, this prohibition would include a wedding (or at least, a wedding which constitutes seudas mitzvah).
The Rema rules that one who does not partake of a Seudas Bris Mila is menudah lashamayim - he doesn't extend this to other seudos mitzva. (See Pischei Teshuva 265.18 who brings the minhag not to extend invitations in order to avoid this outcome)
There are three possible distinctions between seudas bris and other seudos mitzva:
R' Moshe Feinstien (Igros Moshe OCH V2 §96) explains that the Rema understands the curse to be for the zilzul mitzva of not attending the seuda. This applies by seudas bris, which is lkovod
mitzva. However, not attending or partaking of a wedding feast is not a zilzul mitzvah, (because seudas
nessuin is lkovod hachosson vkallah, not lkovod mitzva) and therefore is not included in the curse.
Alternatively, one could suggest the importance of a seudas bris
milah over other seudos mitzva based on the Shaarei Teshuva
(551.15) who cites the Ohr Neelam that it is doiraysa, whereas
other seudos mitzvah are only drabbanan. [The source for seudas
milah being doiraysa is Pirkei D"r Elazar Ch. 29, and Avudraham
(quoted in Beis Yosef YD 265); others quote Nidda 31.]
(- It is worthy to note that the Vilna Gaon held exactly the opposite - that Bris Milah is d'rabbanan and Nissuin is d'oiraysa)
The Chasam Sofer (Shu"t OCH §159) writes that seudas bris milah is not
just a seudas mitzva, but it is a seudas yom tov - the day
becomes a festival, and the feast is the seudas hayom (he explains
accordingly the Rema's psak allowing one who makes a bris to
shave during the sefira).
[See this link (posted by @DoubleAA), which provides a variety of circumstantial reasons why it would not apply to a wedding: 1) Weddings last for considerably longer, and therefore one is not obligated to attend; 2) People generally invite many more people to a wedding, and therefore your attendance is not as important (there are other reasons there, but they will not answer the Rema)]